Interest-Only Loan Calculator

Interest-Only Loan Calculator Guide: Estimate Initial Payment, Later Payment Shock, Remaining Principal, and Total Cost

An interest-only loan separates borrowing cost from principal repayment. During the interest-only period, scheduled payments generally cover the interest accruing on the outstanding principal without materially reducing the amount borrowed.

CFPB defines an interest-only mortgage as a loan with scheduled payments requiring only interest for a specified period. The principal therefore generally remains outstanding while the borrower makes the required interest-only payments.

That creates an important distinction between payment affordability and debt reduction. A $2,000 monthly payment can look substantially cheaper than the payment on a fully amortizing mortgage, but if the entire payment represents interest, the borrower can still owe essentially the original principal years later.

The defining calculation is therefore not just the initial payment. A useful interest-only calculator needs to show two phases: the payment during the interest-only period and the payment required after that period ends.

If the remaining principal is then amortized over a shorter remaining term, the monthly payment can rise sharply even if the interest rate never changes. CFPB specifically identifies the transition from interest-only payments to principal repayment as a reason mortgage payments can increase.

For example, a 30-year loan with a 10-year interest-only period does not necessarily give the borrower 30 additional years to repay principal after year ten. If the original contractual maturity remains 30 years, the full principal may have to amortize over the remaining 20 years. Compressing 30 years of principal into 20 years raises the required payment.

Some interest-only loans introduce an additional risk: the loan can mature before principal has been fully amortized. In that case, a large remaining balance may become due as a balloon payment. CFPB describes balloon payments as large final payments resulting when scheduled payments do not fully repay the loan during the contractual term.

An interest-only loan and a balloon loan are therefore related but not identical. An interest-only loan describes what the borrower is required to pay during a specified phase. A balloon loan describes the existence of a large residual payment at maturity. A loan can contain either feature or both.

Interest-only should also not be confused with negative amortization. If the scheduled payment fully covers all interest due, the principal generally stays unchanged. If the payment is smaller than the interest accruing and unpaid interest is added to principal, the balance grows; that is negative amortization rather than ordinary interest-only treatment.

Rate structure matters too. An interest-only loan can have a fixed rate during the modeled period or can be adjustable. When an adjustable rate rises at the same time the interest-only period ends, the borrower can experience two payment shocks simultaneously: a higher rate and the start of principal repayment.

The correct comparison is therefore not simply “interest-only payment versus normal payment today.” The borrower should compare initial payment, principal remaining at transition, later amortizing payment, total interest, maturity balance, rate sensitivity, and the realistic ability to refinance, sell, or repay the loan if the future payment becomes unaffordable.

How to Calculate an Interest-Only Loan From the Initial Payment Through Final Repayment

Enter the original or current principal: Use the balance that will be outstanding when the interest-only calculation begins.
Enter the interest rate: Use the actual fixed rate or current adjustable rate. If the rate can change, create separate higher-rate scenarios.
Enter the interest-only period: Specify how long the loan requires or permits interest-only payments.
Enter the contractual loan term: The full maturity matters because it determines how much time remains to repay principal after the interest-only period.
Choose fixed or adjustable rate: For an adjustable-rate loan, enter the current rate and one or more future rate assumptions.
Enter any principal paid during the interest-only phase: If voluntary principal payments are planned, reduce the balance entering the later repayment phase accordingly.
Choose the post-interest-only structure: Select full amortization over the remaining term, partial amortization, or balloon maturity according to the loan contract.
Compare the payment before and after transition: The percentage and dollar increase are central affordability outputs.
Review total interest: A lower initial payment does not necessarily mean lower lifetime cost.
Stress-test refinance and sale assumptions: Do not assume that future refinancing or sale proceeds will automatically be available to solve an unaffordable maturity balance.

Formula and variables

During a simple interest-only phase, the periodic payment equals outstanding principal multiplied by the periodic interest rate. If no principal is paid, the principal entering the later repayment phase remains approximately unchanged. The post-interest-only payment is then calculated by amortizing that remaining principal over the number of payments left before maturity. If the loan instead matures with principal still outstanding, the remaining principal becomes part of the final balloon obligation.

Interest-Only Payment = P × r; Post-IO Payment = P × [r(1 + r)^n] ÷ [(1 + r)^n − 1]

P — Outstanding principal: The loan balance on which interest is calculated and which remains due unless principal payments are made.
r — Periodic interest rate: The annual interest rate converted to the applicable payment-period rate.
IO — Interest-only period: The number of months or years during which scheduled payments primarily or exclusively cover interest.
n — Remaining amortization payments: The number of payments available to repay principal after the interest-only phase.
PMTio — Interest-only payment: The modeled payment required to cover interest without scheduled principal reduction.
PMTam — Post-interest-only payment: The principal-and-interest payment required when amortization begins.
B — Balloon balance: Principal or other balance remaining due when the contractual maturity occurs before full amortization.

Scenario 1: $400,000 Mortgage With 10 Years Interest-Only and 20 Years Remaining to Amortize

A borrower takes a $400,000 mortgage at a hypothetical fixed rate of 6.5%. The first 10 years require interest-only payments. The original loan matures after 30 years, so the full $400,000 principal must amortize over the remaining 20 years once the interest-only period ends.

Loan principal: $400,000
Illustrative interest rate: 6.5%
Interest-only period: 10 years
Original contractual term: 30 years
Remaining amortization period: 20 years

Monthly interest rate = 6.5% ÷ 12.
Interest-only payment = $400,000 × 0.065 ÷ 12 ≈ $2,166.67 per month.
If no principal is paid during the first 10 years, the balance entering year 11 remains approximately $400,000.
The $400,000 balance must then amortize over 240 remaining monthly payments.
At 6.5%, the modeled 20-year principal-and-interest payment is approximately $2,983 per month.
The payment increase is approximately $816 per month.
That represents a payment increase of roughly 38% even though the interest rate itself did not increase.

Result: The modeled payment rises from approximately $2,167 during the interest-only phase to about $2,983 when principal repayment begins.

The payment shock comes from compressing repayment of the unchanged $400,000 principal into the remaining 20 years. If the interest rate also increased before amortization began, the later payment would be higher still.

Understanding your results

Interest-only payment

This is the amount required to cover modeled interest during the interest-only phase.

It generally does not reduce principal unless additional principal is voluntarily paid.

Principal remaining after interest-only period

If only interest is paid, this can remain approximately equal to the original balance.

This number is essential because it determines the later amortizing or balloon obligation.

Post-interest-only payment

This is the principal-and-interest payment required after the interest-only phase under the selected amortization structure.

It can be materially higher than the initial payment.

Payment shock

This shows both the dollar and percentage increase when the payment structure changes.

A significant increase can occur even with no interest-rate change.

Total interest

This measures interest paid across both phases.

Delaying principal repayment can increase lifetime interest because a larger balance remains outstanding longer.

Balloon balance

This is the amount still due at maturity when the loan does not fully amortize.

It must be paid from cash, sale proceeds, refinancing, or another source.

Assumptions

The modeled interest-only payment fully covers accrued interest.
No principal reduction occurs during the interest-only phase unless explicitly entered.
The principal entering the repayment phase equals the remaining balance after any voluntary principal payments.
The base scenario assumes the entered interest rate remains constant.
Adjustable-rate scenarios use the user-entered future rate assumptions.
The post-interest-only phase uses standard amortization unless a balloon or other structure is selected.
No missed payments, late fees, or default charges occur.
Taxes, insurance, mortgage insurance, HOA dues, and other housing costs are excluded from principal-and-interest calculations.
The calculator models contractual cash flows rather than determining loan eligibility.

Limitations

Interest-only mortgages can have fixed or adjustable rates, and actual terms vary by lender and contract.
CFPB states that interest-only payments do not reduce the amount owed on the loan during the interest-only period.
The payment after the interest-only phase can be substantially higher because principal repayment begins over the remaining term.
Adjustable-rate interest-only loans can experience payment increases from both a rate reset and the start of principal repayment.
An interest-only loan is different from negative amortization. CFPB regulatory interpretations distinguish interest-only treatment from a payment structure that fails to cover all interest and causes principal to increase.
A loan can contain both an interest-only feature and a balloon payment.
CFPB warns that balloon loans can require a large final payment and that inability to make the payment can place the home at risk.
Refinancing availability cannot be guaranteed. Property value, credit, income, underwriting standards, and market conditions can change before the interest-only period or balloon maturity ends.
Sale proceeds cannot be guaranteed because home values can fall and transaction costs reduce net proceeds.
CFPB identifies interest-only features among mortgage characteristics borrowers should scrutinize carefully when comparing loan offers.
Qualified Mortgage and ability-to-repay rules can restrict or affect certain interest-only and balloon structures. Specific legal treatment depends on the transaction.
The calculator does not determine whether a particular interest-only mortgage is legally permitted, a Qualified Mortgage, or suitable for a particular borrower.

Common mistakes

Assuming a lower initial payment means a cheaper loan.
Assuming interest-only payments reduce principal.
Ignoring the balance remaining when the interest-only period ends.
Assuming the borrower receives a new full 30-year amortization period after ten interest-only years.
Ignoring the original contractual maturity.
Ignoring payment shock.
Ignoring variable-rate risk.
Assuming the future rate will equal today’s rate.
Confusing interest-only with negative amortization.
Confusing interest-only with a balloon loan.
Assuming refinancing will definitely be available later.
Assuming the property can always be sold for enough to repay the balance.
Comparing loans only from their first-year payment.
Ignoring taxes, insurance, HOA dues, and other housing costs when evaluating affordability.

Practical use cases

Scenario 2: Compare interest-only with a fully amortizing mortgage

The borrower compares a low initial interest-only payment with a conventional principal-and-interest payment.

The calculator shows how much monthly cash flow is saved initially and how much principal would have been paid down under the amortizing alternative.

Scenario 3: Rate rises before amortization begins

An adjustable-rate interest-only mortgage enters the principal-repayment phase at a higher rate.

The calculator can isolate the effect of both changes: the rate increase and the start of amortization.

Scenario 4: Make voluntary principal payments during the interest-only phase

The borrower is permitted to pay principal even though only interest is contractually required.

Those additional payments reduce the balance entering the later amortization period and can reduce payment shock.

Scenario 5: Interest-only loan ends in a balloon

The contractual maturity occurs before the remaining principal is fully amortized.

The calculator reports the large residual balance that must be repaid or refinanced at maturity.

Scenario 6: Existing borrower approaches the reset date

The borrower knows the remaining principal, current rate, and number of months until principal repayment begins.

The calculator estimates the upcoming payment rather than waiting for the first higher statement.

Planning and decision guide

Interest-only describes a payment phase, not complete loan economics

CFPB defines the feature by the scheduled requirement to pay only interest for a specified period.

The amount owed therefore generally does not decline during that period.

Scenario 7: Five years of payments, almost no principal reduction

The borrower has made every scheduled payment on time.

If those payments were purely interest-only, the principal can still be essentially the same as when the interest-only phase began.

Principal reduction and payment compliance are different concepts

A borrower can be completely current on the loan while making no meaningful progress against principal.

The calculator should therefore display both payment history and modeled remaining principal.

Interest-only payment is simple when the rate is fixed

Multiply the outstanding principal by the periodic interest rate.

For monthly payments, an annual nominal rate is commonly divided by 12 for a simplified illustration.

Scenario 8: $300,000 at 6%

Annual interest equals approximately $18,000.

The simplified monthly interest-only payment is approximately $1,500.

A lower interest-only payment is created by postponing principal

The borrower is not receiving principal repayment for free.

The missing principal component must be addressed later through amortization, sale, refinance, or maturity payoff.

Scenario 9: $1,500 interest-only versus $2,400 amortizing

The $900 monthly difference creates short-term cash-flow relief.

But the amortizing borrower is simultaneously reducing principal while the interest-only borrower generally is not.

The Mortgage Calculator provides the conventional amortizing benchmark

Run the same principal and rate through the Mortgage Calculator.

Then compare payment, principal reduction, remaining balance, and total interest rather than comparing payment alone.

The later amortization period can be much shorter than the original loan term

If the loan matures 30 years after origination and the first ten years are interest-only, only 20 years remain to repay the principal.

This compressed amortization creates payment shock.

Scenario 10: 10-year IO inside 30-year maturity

The borrower does not receive 40 total years.

Ten years of interest-only plus twenty years of amortization still equals the original 30-year maturity.

Payment shock can occur with a perfectly stable rate

CFPB specifically identifies interest-only loans as mortgages whose payments can increase when borrowers begin paying principal.

The structural payment reset should therefore be calculated even in fixed-rate scenarios.

Scenario 11: Rate unchanged at 6.5%

The interest rate never moves.

The payment still rises substantially because the same principal must now be repaid over fewer years.

Variable rates can create a double reset

An adjustable-rate loan can reprice while the repayment structure also changes.

The borrower can therefore face both a higher interest cost and mandatory principal repayment at the same time.

Scenario 12: 5% during IO, 8% at amortization

The original low payment reflected both an interest-only structure and a lower rate.

The later payment reflects both a higher rate and full principal amortization, producing a much larger jump.

Rate stress should use several scenarios

Show the current rate, a moderate-increase case, and a higher-rate case where the contract permits variability.

A single assumed future rate can conceal the range of possible payment outcomes.

Voluntary principal payments can reduce future payment shock

If the contract permits extra principal payments, paying above required interest reduces the balance exposed to the later amortization schedule.

The benefit is strongest when payments begin early.

Scenario 13: $500 monthly principal during IO

The contractual payment covers interest.

The borrower adds $500 toward principal each month, gradually lowering the balance that will later have to amortize.

Use the Extra Payment Calculator to model voluntary principal reduction

The Extra Payment Calculator can show how recurring or lump-sum principal payments alter balance, interest, and payoff.

For interest-only loans, apply extra payments to the principal trajectory before calculating the reset payment.

Interest-only is not negative amortization

CFPB distinguishes paying all accrued interest from making a payment that fails to cover interest.

If all interest is paid, principal stays level; if unpaid interest is added to principal, debt grows.

Scenario 14: $2,000 interest due, only $1,600 paid

This is not an ordinary interest-only result.

The unpaid $400 can increase the debt balance under a negative-amortization structure if the loan permits it.

The calculator should flag negative amortization separately

Do not silently call a payment interest-only when it does not cover all accrued interest.

The balance-growth mechanism is materially different and riskier.

Interest-only and balloon are also different concepts

Interest-only describes what periodic payments cover.

Balloon describes a large residual payment at maturity.

A loan can contain both features

A borrower can make interest-only payments for several years and then owe most or all principal at maturity.

That structure creates both low periodic payments and a large final obligation.

Use the Balloon Payment Calculator when maturity leaves a residual balance

The Balloon Payment Calculator should focus on the amount remaining at maturity.

This calculator focuses primarily on interest-only payment mechanics and the transition afterward.

CFPB treats balloon payments as a meaningful mortgage risk

CFPB describes balloon payments as large final payments that can represent a significant portion of the loan balance.

If the borrower cannot make the payment or refinance, foreclosure can result.

Scenario 15: $350,000 still due at maturity

The monthly payment looked manageable throughout the loan.

The true maturity obligation is a six-figure payment requiring cash, sale proceeds, or replacement financing.

Refinancing is an option, not a guarantee

CFPB specifically warns interest-only borrowers not to assume they will be able to refinance when the payment increases.

Property values or borrower financial circumstances can deteriorate.

Scenario 16: Property value declines before reset

The borrower expected to refinance before principal payments started.

A lower appraisal and tighter underwriting make replacement financing unavailable, leaving the borrower with the contractual higher payment.

Use the Mortgage Refinance Calculator only after confirming a realistic refinance scenario

The Mortgage Refinance Calculator can compare the existing interest-only loan with a proposed replacement mortgage.

Do not treat that hypothetical refinance as guaranteed future financing.

Sale should not be treated as a guaranteed exit either

A homeowner can plan to sell before the reset or balloon date.

But market value, transaction costs, time to sell, and remaining liens determine whether the sale actually solves the loan balance.

Scenario 17: Planned sale produces less equity than expected

The homeowner assumed appreciation would create a large equity cushion.

A weaker market leaves little sale proceeds after mortgage payoff and selling costs.

Interest-only structures delay equity building from amortization

Home equity can still increase if the property appreciates or the borrower makes voluntary principal payments.

But scheduled interest-only payments themselves generally do not build equity through principal reduction.

Scenario 18: Home value remains unchanged

After five years of pure interest-only payments, the borrower has not gained equity through scheduled amortization.

A fully amortizing borrower would ordinarily owe less principal after the same period.

The Amortization Calculator makes the opportunity cost visible

Compare the interest-only balance after five or ten years with the balance of an amortizing loan.

The Amortization Calculator shows the principal that would have been retired under conventional repayment.

Total interest can be materially higher

Interest is calculated from outstanding principal.

Keeping principal high for years means interest continues to be charged against a larger balance for longer.

Scenario 19: Same rate, same ultimate maturity

The interest-only borrower keeps the original principal outstanding during the initial phase.

The amortizing borrower steadily reduces the balance, causing future interest charges to fall sooner.

Do not compare only cumulative payments during the first few years

Interest-only can appear dramatically cheaper early because principal repayment has been postponed.

The correct horizon extends through maturity or payoff.

Scenario 20: Five-year comparison favors IO only superficially

The interest-only borrower paid less cash during the first five years.

But still owes substantially more principal, so the apparent savings partly represent deferred repayment rather than economic gain.

Other housing costs remain due during the interest-only period

Property taxes, homeowners insurance, mortgage insurance where applicable, HOA dues, maintenance, and other housing costs do not disappear because the mortgage payment is interest-only.

Affordability should use the complete housing budget.

Use the Home Affordability Calculator for the broader household commitment

The interest-only loan calculator shows mortgage principal-and-interest structure.

The Home Affordability Calculator should include taxes, insurance, debt obligations, and broader affordability inputs.

A low introductory payment can distort affordability analysis

If the household can afford the property only while principal payments are postponed, the later reset is central to affordability.

CFPB advises borrowers to focus on a mortgage that fits their actual budget rather than merely the amount a lender will offer.

Scenario 21: Comfortable at $2,000 but not $3,400

The household evaluates only the interest-only payment.

If the scheduled reset payment would exceed sustainable cash flow today, relying on future income growth introduces additional risk.

Interest-only can be useful for specialized cash-flow needs but does not remove principal

Some borrowers may value temporary payment flexibility because income is irregular or capital is deliberately allocated elsewhere.

The calculator should quantify the tradeoff without assuming the strategy is inherently good or bad.

Scenario 22: Seasonal business owner

The borrower values lower required payments during an early business-expansion period.

The financial plan remains viable only if the later principal obligation is deliberately funded rather than ignored.

Opportunity-cost claims require realistic alternative returns

A borrower may argue that money not used for principal can be invested elsewhere.

That comparison should use after-tax, risk-adjusted assumptions rather than assuming investment returns will automatically exceed the mortgage rate.

Scenario 23: Invest payment difference

The borrower invests the difference between interest-only and amortizing payments.

The investment can outperform, underperform, or lose value, while the mortgage principal remains contractually due.

Interest-only can appear in home-equity borrowing too

Some HELOC draw periods can use interest-oriented minimum payment structures.

But HELOCs add revolving-credit and variable-draw mechanics that make them a separate calculator.

Use the HELOC Calculator when the loan is revolving

The HELOC Calculator models credit limits, amount drawn, CLTV, draw period, repayment period, and variable-rate exposure.

Use Interest-Only when the primary question is the payment structure itself.

Interest-only loans deserve comparison against a less risky structure

CFPB currently advises borrowers who encounter risky features such as interest-only or balloon payments to ask the lender for a Loan Estimate for an alternative without the feature so costs can be compared.

The calculator should facilitate the same side-by-side comparison.

The strongest result is a two-phase timeline

Show payment during the interest-only period, principal remaining at transition, post-reset payment, percentage payment increase, total interest, maturity date, and any balloon amount.

That makes the future obligation as visible as the attractive initial payment.

Frequently asked questions

What is an interest-only loan?

CFPB defines an interest-only mortgage as one with scheduled payments that require only interest for a specified period. The amount owed generally does not decline from those payments alone.

How do I calculate an interest-only payment?

For a simplified fixed-rate monthly calculation, multiply principal by the annual interest rate and divide by 12.

What is the monthly payment on a $300,000 interest-only loan at 6%?

The simplified interest-only payment is approximately $1,500 per month before taxes, insurance, and other housing costs.

Does an interest-only payment reduce principal?

No if the payment covers only accrued interest. The principal remains outstanding unless additional principal is paid.

What happens when the interest-only period ends?

CFPB states that the borrower may begin making higher monthly payments that include principal, repay the loan balance, or refinance if refinancing is available.

Why does the payment increase after interest-only ends?

Principal repayment begins, often over fewer years than a conventional loan would have had from origination. The rate may also change if the loan is adjustable.

What is payment shock?

It is a substantial increase in required payment when the loan transitions from one payment structure or rate to another.

Can the payment increase even if my rate does not change?

Yes. CFPB specifically notes that interest-only borrowers can experience higher payments when they begin repaying principal.

Is an interest-only loan cheaper?

Not necessarily. It can have a lower initial payment but may generate more total interest because principal remains outstanding longer.

Is interest-only the same as negative amortization?

No. Interest-only payments cover accrued interest so principal generally stays unchanged. Negative amortization occurs when payments do not cover all interest and the balance increases.

Can an interest-only balance grow?

Not under a true interest-only structure when all accrued interest is paid. If unpaid interest is added to principal, the loan has a negative-amortization feature.

Is an interest-only loan the same as a balloon loan?

No. Interest-only describes periodic payment structure. Balloon describes a large remaining payment due at maturity. A loan can contain both.

Can an interest-only mortgage have a balloon payment?

Yes if principal remains due when the contractual loan term ends.

How do I calculate the balloon after interest-only payments?

Calculate the principal remaining at maturity. If no principal was repaid, the balloon can remain close to the original principal. Use the Balloon Payment Calculator for the residual-balance analysis.

Are interest-only mortgages fixed rate?

They can be fixed or adjustable depending on the loan contract.

What happens if the rate increases?

The interest-only payment can rise, and the later amortizing payment can become even larger.

What is an interest-only ARM?

It is an adjustable-rate mortgage that also permits or requires interest-only payments for a defined period.

Can I make principal payments during the interest-only period?

Often yes if permitted by the loan terms. Extra principal reduces the balance that must later be amortized or repaid.

Should I pay principal during the interest-only period?

Doing so generally reduces future interest and payment shock, but the appropriate decision depends on your broader finances and loan terms.

How much principal will I owe after five years interest-only?

If you made only required interest payments and no principal payments, the balance can remain approximately equal to the starting principal.

How much principal will I owe after ten years interest-only?

Again, if no principal was repaid, the balance can remain close to the amount outstanding when the interest-only period began.

Does a 30-year loan with 10 years interest-only become a new 30-year loan afterward?

Not necessarily. If the contractual maturity remains 30 years from origination, only 20 years remain to repay principal after the first ten years.

Can I refinance before the interest-only period ends?

Potentially, if you qualify and suitable refinancing is available. CFPB warns borrowers not to assume future refinancing will necessarily be possible.

Why might refinancing not be available?

Home value, income, credit, interest rates, underwriting standards, debt levels, or other circumstances can change.

Can I sell the home before the reset?

Yes, but the sale must generate enough proceeds to address the mortgage and transaction costs. Future property value cannot be guaranteed.

Does interest-only build home equity?

Not through scheduled principal reduction. Equity can still increase through property appreciation or voluntary principal payments.

How does interest-only compare with a normal mortgage?

A conventional amortizing mortgage pays both principal and interest from the beginning. Use the Mortgage Calculator for the comparison.

How much principal would a normal mortgage have paid down?

Use the Amortization Calculator to compare the conventional remaining balance at the same future date.

Can extra payments reduce interest-only risk?

Yes. Applying additional money to principal reduces the later balance and future interest. Use the Extra Payment Calculator for detailed payoff scenarios.

Is an interest-only HELOC the same as an interest-only mortgage?

Not exactly. HELOCs are revolving lines of credit with draw and repayment periods. Use the HELOC Calculator for the revolving structure.

Are interest-only mortgages risky?

They can carry greater payment and refinancing risk because principal repayment is postponed. CFPB specifically identifies interest-only features among mortgage characteristics borrowers should examine carefully.

Are interest-only mortgages Qualified Mortgages?

Interest-only features can affect treatment under federal Qualified Mortgage and ability-to-repay rules. Eligibility depends on the specific loan and regulatory requirements.

Does this payment include property taxes and insurance?

No unless those inputs are explicitly added. The interest-only calculation ordinarily describes principal-and-interest mechanics only.

Should I compare the interest-only payment with total housing cost?

Yes. Property tax, insurance, mortgage insurance, HOA dues, maintenance, utilities, and other costs can materially affect affordability.

Can interest-only make sense for variable income?

Some borrowers value temporary payment flexibility, but future principal repayment remains mandatory. The calculator should quantify the later obligation rather than assuming future income will solve it.

How accurate is an interest-only loan calculator?

The mathematics can be precise for the entered principal, rate, term, and structure. Actual payments can differ because of adjustable rates, daily-interest conventions, fees, contractual payment rules, escrow, future principal payments, and other loan terms.

Sources and review

What is an "interest-only" loan? — Consumer Financial Protection Bureau. Accessed 2026-08-31.
Why did my monthly mortgage payment go up or change? — Consumer Financial Protection Bureau. Accessed 2026-08-31.
What is a balloon payment? When is one allowed? — Consumer Financial Protection Bureau. Accessed 2026-08-31.
What is an option or payment-option ARM? — Consumer Financial Protection Bureau. Accessed 2026-08-31.
Understand the Different Kinds of Loans Available — Consumer Financial Protection Bureau. Accessed 2026-08-31.
Loan Estimate Explainer — Consumer Financial Protection Bureau. Accessed 2026-08-31.
Regulation Z § 1026.43 — Minimum Standards for Transactions Secured by a Dwelling — Consumer Financial Protection Bureau. Accessed 2026-08-31.
Official Interpretation of Regulation Z § 1026.43 — Consumer Financial Protection Bureau. Accessed 2026-08-31.

Reviewed 2026-08-31 by Dr Akawak Ejigu, DBA.

Interest-only loan phases