Work out story estimation confidence instantly with clear inputs, formula shown and shareable results.
PERT combines three-point estimates as (optimistic + 4 x likely + pessimistic) / 6, with standard deviation (pessimistic - optimistic) / 6. The value is that it produces both a central estimate and an uncertainty range, so commitments can be made at a stated confidence level rather than on a single number that is optimistic by construction.
PERT estimate
expected = (O + 4M + P) / 6; sd = (P - O) / 6; 95th percentile = expected + 1.645 x sd
PERT approximates a beta distribution where the mode carries most of the information while the extremes bound it. The weights make the mean tractable to compute.
No. The expected value is met roughly half the time. Commit at the 80th or 95th percentile and treat the difference as schedule buffer.