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PERT Calculator

An interactive PERT calculator. Enter optimistic, most likely, and pessimistic estimates to calculate the expected duration, standard deviation, and variance for any project task.
About This Calculator

This calculator applies the PERT formula to three time estimates to produce a weighted expected duration and measure of uncertainty. Enter the optimistic (best case), most likely (expected case), and pessimistic (worst case) durations for any task. The calculator returns the expected duration (tE = (O + 4M + P) / 6), standard deviation (σ = (P minus O) / 6), and variance (σ squared).

The PERT (Program Evaluation and Review Technique) Formula

Expected Duration (tE) = (O + 4M + P) / 6 | Standard Deviation (σ) = (P minus O) / 6 | Variance = σ squared

How to Use This Calculator

Enter three estimates for any task: the optimistic duration (best realistic case), the most likely duration (expected case under normal conditions), and the pessimistic duration (worst realistic case). The calculator applies the PERT formula to produce the expected duration, standard deviation, and variance.

Interpreting the Results

The expected duration is your planning estimate. The standard deviation tells you how uncertain that estimate is. One standard deviation on either side of the expected value captures approximately 68% of possible outcomes. Two standard deviations capture 95%. A task with an expected duration of 10 days and a standard deviation of 2 days has a 95% probability of finishing between 6 and 14 days.

Store three point estimates in Custom Fields and use formula fields for automatic PERT calculations.
Estimate Tasks in ClickUp

Common Questions About PERT Calculator

What inputs does a PERT calculator need?
Three time estimates: optimistic (best realistic case), most likely (expected case), and pessimistic (worst realistic case). These should represent genuinely different scenarios, not arbitrary adjustments around a single guess.
How do I use the standard deviation from this calculator?
The standard deviation measures estimate uncertainty. Add and subtract one standard deviation from the expected duration to get the 68% confidence range. Add and subtract two standard deviations for the 95% range. Higher standard deviation means more uncertainty in the estimate.