What
PERT gives a weighted expected duration and a rough sigma from O/M/P.
Estimation
PERT estimator
PERT gives a weighted expected duration and a rough sigma from O/M/P.
Enter O ≤ M ≤ P to get TE and confidence intervals.
PERT estimator
Inputs
Results
Expected time (TE)
—
σ
—
~68% CI low
—
~68% CI high
—
~95% CI low
—
~95% CI high
—
Chart
Guide
Three-point engineering estimates
Why
Single-point estimates are usually optimistic.
How
Enter O ≤ M ≤ P to get TE and confidence intervals.
Formula: TE = (O + 4M + P) ÷ 6 · σ = (P − O) ÷ 6
Go deeper
Why you’ll love this
Single-point estimates are usually optimistic — use three points.
How to jump in
-
O / M / P
Keep O ≤ M ≤ P.
-
TE and σ
Expected time and spread.
-
Confidence bands
Rough 68% and 95% ranges.
What you walk away with
- Classic PERT formula
- CI bands
- Bar chart
- Free
Where it shines
Task estimates
Replace one hopeful number.
Schedule risk
See the O-to-P gap.
With timeline
Feed TE into project plans.
Quick answers
What unit?
Any consistent unit (hours/days).
Exact statistics?
A common engineering approximation, not a formal hypothesis test.