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.

Try it with a real decision

Start with the example. Make it yours.

The numbers below are an editable example. Replace them with your own duration estimates; the answer updates as you type. Everything stays in this browser.

New to three-point estimates?

Optimistic: what it takes when things go well, without assuming a miracle.
Most likely: the outcome you would expect most often on similar work.
Pessimistic: a realistic difficult outcome. Include uncertainty, not an arbitrary markup.

Keep all three in the same units and put the most likely value between the other two. P80 means an estimated 80% chance of staying at or below a number under this model; it is not a promise.

These quick tools use a normal approximation, not simulated samples. The approximation can extend beyond your optimistic and pessimistic bounds, particularly for skewed estimates. For bounded task sampling, dependencies and separate risk events, use the full app.

Duration estimate & deadline

Duration — optimistic (O) days

Duration — most likely (M) days

Duration — pessimistic (P) days

How is the deadline set?

Deadline (days from start)

Results

Probability you finish on time91.9%

Deadline (days used)60

Days to finish you can expect to stay at or under (normal approximation)
Scenario	P50	P80	P90
Days to finish	48 d	55 d	59 d

P50 duration means 50% of outcomes finish in that time or less — budgeting the schedule at P50 is roughly a coin flip. Your on-time probability 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.

Test an alternative

What changes if…?

Keep these results, then adjust an estimate above to compare. Your baseline stays in this tab until you clear it or reload. Values are rounded for display.

Plain text with your assumptions, key results and any saved baseline. No account needed.

No baseline yet. Keep a result you would like to compare.

Continue with the whole project

Turn one duration into a connected schedule

Create tasks, connect their dependencies, and compare deadlines in Schedule Lab. Parallel work and tasks on the critical path affect completion differently.

A single duration cannot show which dependency controls the finish date. Calendar dates here use elapsed days, not a business-day calendar. All outputs remain conditional on the assumptions you enter.

Start with a project template Explore the full app →

A date is cheap to promise; knowing which date you can defend is the expertise. Recommended reading: How to Remain Valuable When Intelligence Becomes Cheap .