Estimating tool

PERT Three-Point Estimating Calculator

Calculate a weighted expected duration from optimistic, most-likely, and pessimistic estimates.

Museum estimate lab

Move three estimates. Watch the weighted answer shift.

Try a preset or adjust the three estimates.

Three-point estimate

The controls preserve O ≤ M ≤ P. Values represent days for one uncertain activity.

6 days
Favorable conditions that are still realistically possible.
10 days
The duration expected to occur most often.
20 days
Unfavorable conditions that are still realistically possible.

Live estimate

PERT expected durationEnable JavaScript for the live estimate.Most likely receives four of the six weights.
(O + 4 × M + P) ÷ 6
OMMMMP
Ordinary averageNot calculated
Standard deviationNot calculated
VarianceNot calculated

Enable JavaScript to update the estimate.

Important: PERT is an estimating model, not a promise. Its usefulness depends on realistic inputs and sound schedule logic.

For the worked example and reasoning, read the related study guide.

How it works

Provide optimistic, most-likely, and pessimistic durations. PERT gives the most-likely estimate four times the weight of either outer estimate.

Example to try

With 6 optimistic days, 10 most-likely days, and 20 pessimistic days, the weighted estimate is 11 days while the ordinary average is 12 days.

Read the result

The expected duration is an estimate rather than a promised deadline. Standard deviation and variance describe the spread between the optimistic and pessimistic cases.