Expected time (o + 4m + p) / 6 and a (p − o) / 6 spread.
| Expected | – |
| Spread | – |
Use this calculator for a three-point PERT estimate. Enter optimistic, most likely, and pessimistic durations in the same unit (days, hours, whatever you use).
Expected te = (o + 4m + p) / 6. Spread sd = (p − o) / 6. Optimistic 4, most likely 6, pessimistic 12 gives 6.667 expected and 1.333 spread. Paths in a network are extra; this is one activity.
Optimistic: Best case.
Most likely: Usual case.
Pessimistic: Worst case.
Expected: Weighted mean.
Spread: (p − o) / 6, a PERT standard-deviation sketch.
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