PERT estimation

three-point estimate (O + 4M + P)/6, σ, and deadlines at P50/P80/P90 confidence

Tasks (days)

TaskOMP

O — optimistic, M — most likely, P — pessimistic estimate in days. E = (O+4M+P)/6, σ = (P−O)/6.

Result

Expected duration (P50)

14,20 d

σ = 1,70 d

P80 (enough in 80% of cases)15,60 d

P90 (cautious deadline)16,40 d

P95 (conservative)17,00 d

API endpoints5,30 ± 1,00

Frontend6,70 ± 1,30

Tests & deploy2,20 ± 0,50

Task durations are distributed around E; the σ of the sum is the root of summed variances (tasks assumed independent). The classic mistake is quoting the client the sum of "most likely" estimates — that's ~P30, a 70% chance of missing. Promise P80–P90, track P50 as the internal plan.

About Pert

Pert — free online tool on usefulhub.cloud. IT Tools: Developer utilities. Use our tools without registration or installing software. All calculations happen in your browser — your data is never sent to a server.