Construction scheduling and critical-path guide
A network schedule connects activities with logical predecessors. A forward pass finds early dates and the minimum completion date; a backward pass identifies total float and the critical path.
This calculator provides a compact deterministic model. A controlled project schedule also needs validated scope, calendars, constraints, resources, risks, status updates and change control.
How to build a preliminary CPM schedule
- Choose the start: Enter the planned project start date; weekend dates roll to Monday.
- List measurable activities: Use clear activity names and realistic whole-workday durations.
- Connect the logic: Enter predecessor IDs that must finish before each activity begins.
- Review the network: Resolve missing predecessors, duplicate IDs and circular logic.
- Validate the result: Review critical activities, float and forecast dates with the project team.
Formula and variables
Activities with zero total float form the controlling path in this unconstrained finish-to-start network.
Early start = latest predecessor finish + 1; early finish = early start + duration − 1; total float = late start − early start- Duration — Activity duration
- Whole working days required for the activity.
- Predecessor — Logical dependency
- Activity that must finish before its successor starts.
- Float — Total float
- Working days an activity can slip before delaying the modeled project finish.
Worked example: two parallel branches
Activity A takes 5 days. B takes 3 days after A, C takes 2 days after A, and D takes 4 days after both.
- Start
- Monday, August 3, 2026
- Long branch
- A → B → D
- Short branch
- A → C → D
- A finishes after 5 workdays.
- B and C then run in parallel.
- D waits for the later predecessor, B.
Result: The schedule is 12 workdays; A, B and D are critical, while C has 1 workday of float.
A one-day delay to a zero-float activity delays the modeled finish unless logic or durations change.
Understanding your results
Minimum duration
The deterministic span implied by durations, logic and the weekday calendar.
Critical path
The zero-float sequence controlling the forecast finish in this model.
Total float
Modeled scheduling flexibility, not time owned exclusively by one party.
Assumptions
- All relationships are finish-to-start with zero lag.
- Work occurs Monday through Friday.
- Each activity duration is a positive whole number of workdays.
- Resources are available whenever logic permits work to start.
Limitations
- Holidays, shutdowns, weather calendars and shifts are not modeled.
- Resource leveling, leads, lags, constraints and progress status are excluded.
- Deterministic durations do not quantify schedule uncertainty.
- The result is not a contractual baseline or update.
Common mistakes
- Leaving activities without necessary predecessors.
- Using overly broad activities that hide sequencing risk.
- Adding date constraints instead of complete logic.
- Treating total float as fixed or privately owned.
- Failing to update actual progress and remaining duration.
Practical use cases
Concept schedule
Test a proposed work sequence before developing a detailed baseline.
What-if review
Change activity durations or logic to see which path controls completion.
Team coordination
Use the dated activity table to discuss handoffs and missing scope.
Planning and decision guide
Build complete logic
GAO guidance emphasizes a comprehensive, well-constructed schedule with logically sequenced activities.
Confirm the critical path
The longest continuous sequence determines earliest completion and deserves management attention.
Manage float and uncertainty
Review low-float paths and perform schedule-risk analysis in a suitable project scheduling system for material commitments.
Frequently asked questions
Does the calculator skip weekends?
Yes. It uses a Monday-through-Friday calendar and does not include holidays.
What makes an activity critical?
In this unconstrained model, an activity is critical when its calculated total float is zero.
Can activities run in parallel?
Yes. Activities may start together when their own predecessor requirements are satisfied.
What is a circular dependency?
It occurs when a chain of activities ultimately depends on itself, making the schedule impossible to resolve.
Is this a contract schedule?
No. It is a preliminary planning model and omits many controls required for a maintained contractual schedule.
Sources and review
- GAO Schedule Assessment Guide: Best Practices for Project Schedules — U.S. Government Accountability Office. Accessed 2026-07-18.
- Critical Path Method Calculations and Schedule Terminology — Project Management Institute. Accessed 2026-07-18.
Reviewed 2026-07-18.