Property tax calculator: from assessed value to an annual estimate
Property tax is generally calculated from a taxable assessed value and one or more local levies. Market value, assessed value, and taxable value can be different numbers. The relationship depends on the jurisdiction's assessment ratio, exemptions, caps, classifications, and reassessment process.
This calculator first multiplies market value by the assessment ratio, subtracts the exemption amount without allowing taxable value below zero, and applies the combined tax rate. It also divides annual tax by 12 and compounds the entered annual increase for a planning projection.
The difficult part is not the arithmetic; it is obtaining the correct local inputs. Use the assessor and taxing-authority records for the property. The worked examples explain the calculation, but no example jurisdiction is a substitute for your own assessment notice and tax bill.
Translate local property-tax rules into calculator inputs
- Identify the value basis: Find the relevant market, appraised, or estimated value from the local assessor rather than assuming the purchase price is always the tax value.
- Confirm the assessment ratio: Enter the local percentage used to convert the selected value basis to assessed value.
- Verify eligible exemptions: Use exemptions that apply to the owner and property, and confirm whether they reduce value or operate through another mechanism.
- Combine compatible local rates: Add applicable taxing-authority rates only when they are expressed against the same taxable base.
- Convert mills correctly: Divide mills by 10 to enter a percent: 20 mills equals 2.0%.
- Choose a projection assumption: Use the annual increase only as a scenario; it is not a prediction of assessments, levies, or law.
- Reconcile with the official bill: Compare the estimate with assessor records and the latest tax bill, including special charges or discounts the model omits.
Formula and variables
The combined rate must use the same value base and units as the local rule. The calculator expects a percentage; one mill equals 0.1%, or one dollar per $1,000 of taxable value.
Assessed value = market value x assessment ratio; Taxable value = max(assessed value - exemptions, 0); Annual tax = taxable value x combined tax rate- Market value — Estimated property value
- The value to which the entered assessment ratio is applied. (dollars)
- Assessment ratio — Share converted to assessed value
- A locally defined percentage; use 100% only when that matches the applicable system. (percent)
- Exemptions — Reduction in assessed value
- The total eligible value reduction modeled before the tax rate is applied. (dollars)
- Combined tax rate — Total entered levy rate
- The sum of applicable rates that use the modeled taxable-value base. (percent)
Worked example: assessment ratio and exemption both matter
A property has a $425,000 market value, an 80% assessment ratio, a $40,000 exemption, a 2.1% combined rate, and a 3% annual projection assumption.
- Market value
- $425,000
- Assessment ratio
- 80%
- Exemption
- $40,000
- Combined rate
- 2.1%
- Assessed value is $425,000 x 80%, or $340,000.
- Taxable value is $340,000 minus $40,000, or $300,000.
- Annual tax is $300,000 x 2.1%, or $6,300.
- The monthly planning amount is $6,300 divided by 12, or $525.
Result: Estimated annual property tax: $6,300
The effective tax as a share of market value is about 1.48%, which is lower than the 2.1% statutory input because the assessment ratio and exemption reduce the taxable base.
Understanding your results
Assessed and taxable value
Assessed value reflects the entered ratio. Taxable value subtracts the entered exemption and cannot fall below zero. Confirm that local exemptions actually operate this way.
Annual tax and monthly planning amount
The annual result is taxable value multiplied by the combined rate. The monthly figure is annual tax divided by 12, not necessarily the exact escrow amount on a mortgage statement.
Effective rate and projection
The effective rate compares modeled tax with market value. The projection compounds one constant increase and should be read as a stress test rather than a government forecast.
Assumptions
- The entered market value is the correct starting value for the local assessment ratio.
- All entered exemptions reduce assessed value as a single dollar amount.
- The combined percentage rate applies uniformly to the calculated taxable value.
- The annual estimate is divided evenly by 12 for monthly planning.
- The projection compounds the same increase once per year.
- No discounts, penalties, credits, refunds, or special assessments modify the result.
Limitations
- The calculator cannot identify the correct assessment system, exemptions, or rates for a location.
- Assessment caps, levy limits, classification rules, and phased reassessments are not modeled.
- Special assessments, parcel charges, fees, discounts, and delinquency penalties are excluded.
- Some exemptions or credits may not operate as a simple reduction in assessed value.
- The combined rate may be invalid if local levies use different tax bases.
- The monthly result is not an escrow analysis and excludes insurance or an existing escrow shortage.
- The annual growth projection is not a forecast of legislation, assessments, or local budgets.
Five-year projection: compounding a planning assumption
Continue the first example and project the $6,300 annual estimate for five years using a constant 3% annual increase.
- Starting annual tax
- $6,300
- Annual increase assumption
- 3%
- Projection period
- 5 years
- Future tax is $6,300 x 1.03 to the fifth power.
- The resulting fifth-year planning amount is about $7,303 annually.
- That is about $609 per month if divided evenly by 12.
Result: Projected fifth-year tax: about $7,303
This smooth projection is a budgeting scenario only. Reassessments, levy changes, caps, exemptions, and special assessments can create a very different path.
Common mistakes
- Applying the tax rate directly to market value when an assessment ratio applies.
- Using the purchase price without checking the assessor's value and reassessment rules.
- Entering mills as a percentage without converting the units.
- Assuming every advertised exemption applies automatically.
- Combining rates that use different taxable-value bases.
- Using an old rate with a new assessment, or vice versa.
- Treating annual tax divided by 12 as the exact mortgage escrow payment.
- Ignoring special assessments or parcel charges shown separately on the bill.
Practical use cases
Evaluate a home before purchase
Use current assessor records, but also investigate whether the sale can trigger reassessment or alter exemptions. The seller's existing bill may not represent the buyer's future bill.
Review an assessment change
Enter the previous and new assessed-value assumptions separately to isolate the dollar effect. Follow the jurisdiction's review or appeal instructions and deadlines if records appear incorrect.
Planning and decision guide
Start with primary local records
Use the assessor's parcel record, exemption status, taxing-authority rates, and latest bill. Aggregator estimates may use stale values or incomplete levies.
Ask what changes after a sale
Purchase, occupancy, ownership, and application deadlines can affect assessment and exemptions. Research the rules before relying on the seller's payment.
Keep rate and value dates aligned
A value from one tax year combined with rates from another can create a misleading estimate. Record the effective period for every input.
Separate the tax bill from escrow
Escrow payments can include insurance and a shortage or surplus adjustment. Reconcile the tax component with the official bill before diagnosing a payment change.
Budget for uncertainty
Use a higher assessment or rate scenario when buying into a changing market, completing improvements, or approaching reassessment.
Continue planning
Estimate home affordability
See how the tax estimate changes the full housing payment and price range.
Compare rent and buying
Include property tax in a longer-term net housing-cost comparison.
Build a mortgage payment
Combine financing with the ownership costs relevant to your property.
Estimate closing costs
Plan upfront cash separately from recurring property tax.
Frequently asked questions
Is assessed value the same as market value?
Not necessarily. Local rules determine how market, appraised, assessed, and taxable values relate. Use the terminology and records for the property's jurisdiction.
How do I convert mills to a percentage?
One mill is $1 per $1,000 of taxable value, which equals 0.1%. Divide the mill rate by 10 to enter a percentage.
How do exemptions affect the calculation?
This model subtracts the entered exemption amount from assessed value. Verify eligibility and calculation method because local exemptions can work differently.
Why is the effective rate different from the entered rate?
The entered rate applies to taxable value. The effective rate compares tax with market value, so an assessment ratio or exemption can make it lower.
Can property tax change after I buy a home?
Yes. Reassessment, ownership changes, expiring exemptions, levy changes, improvements, or local rules can change the bill. Research the specific jurisdiction.
Is monthly property tax the same as escrow?
Not always. Escrow may also include insurance and adjustments for projected bills, shortages, or surpluses.
Does the calculator include special assessments?
No. Add those separately when reviewing the official bill or property disclosures.
Is the multi-year projection a forecast?
No. It compounds one user-entered annual increase to create a planning scenario. Actual values and rates may change unevenly.
Sources and review
- Property Tax Basics — Texas Comptroller of Public Accounts. Accessed 2026-08-31.
- What is an escrow or impound account? — Consumer Financial Protection Bureau. Accessed 2026-08-31.
- Loan Estimate explainer — Consumer Financial Protection Bureau. Accessed 2026-08-31.
Reviewed 2026-08-31 by Dr Akawak Ejigu, DBA.