PERT Project Duration Calculator
The PERT duration calculator converts optimistic, most likely and pessimistic task estimates into an expected duration and a simple uncertainty estimate.
How to use this calculator
- Enter non-negative estimates in the same units with optimistic ≤ most likely ≤ pessimistic.
- Check the units and definitions before comparing results with another source.
- Change one input at a time when comparing scenarios, and keep the reporting period and assumptions consistent.
Formula used by the project duration pert calculator
Expected duration = (O + 4M + P)/6; estimated standard deviation = (P − O)/6
- Expected duration = (O + 4M + P)/6; estimated standard deviation = (P − O)/6
- This is a task-level approximation. It does not calculate a project critical path or fully account for dependency, resource and schedule risks.
- Inputs are checked for required values and valid ranges; displayed results are rounded for readability.
Worked examples
Worked example
Optimistic 3 days, most likely 5 days and pessimistic 11 days.
Expected duration is (3 + 4×5 + 11)/6 = 5.667 days; estimated standard deviation is 1.333 days.
Expected duration is (3 + 4×5 + 11)/6 = 5.667 days; estimated standard deviation is 1.333 days.
Understanding the result
The PERT duration calculator converts optimistic, most likely and pessimistic task estimates into an expected duration and a simple uncertainty estimate.
This is a task-level approximation. It does not calculate a project critical path or fully account for dependency, resource and schedule risks.
Important notes
This is a task-level approximation. It does not calculate a project critical path or fully account for dependency, resource and schedule risks.
The result applies to the numbers and assumptions entered here; verify specifications for safety-critical or regulated uses.
Frequently asked questions
Why is the most-likely estimate weighted four times?
The conventional PERT approximation gives the most-likely estimate extra weight when calculating the expected duration.
Does the output predict a guaranteed finish date?
No. It is an estimate based on three scenarios and not a schedule guarantee.
How do I use this calculator?
Enter non-negative estimates in the same units with optimistic ≤ most likely ≤ pessimistic.
Affiliate recommendations
Tools related to PERT Project Duration Calculator
These tools are selected for the calculator topic. The Calc Studio may earn a commission from purchases made through affiliate links.
- BusinessAnywhere business services Visit partner ↗
Business formation and business services for entrepreneurs and online businesses.
See the Affiliate Disclosure for details.
Related calculators
- Project Progress Calculator — Calculate simple task-count completion as a percentage of total project tasks.
- Full-Time Equivalent Calculator — Convert weekly workload hours into full-time equivalent staffing units using a chosen standard work week.
- YouTube RPM Revenue Estimator — Estimate illustrative creator revenue from views and an assumed RPM, or calculate observed RPM from actual revenue.
- Average Selling Price Calculator — Calculate net average selling price per unit from revenue and units sold over a matching period.
- Cost per Lead Calculator — Calculate campaign cost per lead from advertising spend and a consistent lead count.
- Current Ratio Calculator — Calculate the current ratio and working capital from current assets and current liabilities.
Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
- How to Calculate Salary from an Hourly Rate — Convert hourly pay into weekly, monthly, and annual estimates and understand the assumptions behind the result.
- How to Calculate a Z-Score — Learn how a z-score shows how far a value is from the mean in standard-deviation units.
- Salary — Understand salary, hourly pay, annual gross pay estimates, and the assumptions behind salary conversions.
This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.