How likely are we to actually hit the deadline?
If your duration estimate is uncertain, a deadline is a bet, not a promise. Find out the real probability you finish on time — and the day you should plan around if you want an 80% chance of being safe.
The work is expected to take about 48 days, and you finish within a 60-day deadline in about 91.9% of outcomes. To hold an 80% chance, plan the schedule around about 55 days, not 48.
Duration estimate & deadline
Results
| Scenario | P50 | P80 | P90 |
|---|---|---|---|
| Days to finish | 48 d | 55 d | 59 d |
P50 of 48 days means 50% of outcomes finish in that time or less — budgeting the schedule at P50 is roughly a coin flip. An 91.9% on-time figure for a 60-day deadline may or may not be enough for your client; decide what confidence you need.
Formula
P(finish ≤ deadline) = Φ((deadline − mean) / σ)
finish days at P = mean + z·σ, with mean = (O + 4M + P)/6, σ = (P − O)/6
Normal approximation: probabilities use a normal approximation to a Beta-PERT duration — a fast, honest single-estimate shortcut.
Related tools
- P50 vs P80 — which number to plan around
- Turn a three-point estimate into P50/P80/P90
- What must we quote to break even?
- How likely are we to blow the budget?
A single duration misses how tasks and dependencies really chain together. For a delivery date you can stand behind across the whole project, run the full app or read the methodology.