Turn one three-point estimate into honest P50, P80 and P90 numbers
Most underpriced bids and missed deadlines start from quoting a single optimistic number. A PERT estimate lets you say “probably about 65 hours, and to be 80% sure we plan for about 75” — a range you can defend instead of a coin flip.
Your best single-point estimate is about 65 hours. To have an 80% chance of staying at or under a number, plan for about 75 hours.
Your three-point estimate
Estimates entered here. Pessimistic (P) must be at least as large as optimistic (O).
Planning values
Meaning of the language: P80 = 80% of simulated outcomes fall at or below this value. Budgeting at P50 leaves you ~50% likely to go over.
Formula
PERT mean = (O + 4M + P) / 6 (Beta-PERT with weighting λ = 4)
standard deviation ≈ (P − O) / 6
P50 ≈ mean · P80 ≈ mean + 0.84·σ · P90 ≈ mean + 1.28·σ
Normal approximation: the P50/P80/P90 above are computed from a normal approximation to the Beta-PERT distribution — a fast, honest approximation for planning. It is a single-estimate shortcut; for a full multi-task, multi-risk view use the app below.
Related tools
- Will this fixed-price project actually make money?
- What should I bid to keep my target margin?
- How likely are we to hit the deadline?
- What must we quote just to break even?
PERT on one task is a start. For a whole project with dependencies, cost assumptions and risk events, run thousands of scenarios instead: try the full app, or read how the math works on the methodology page.