Project Duration Calculator: How to Estimate Timelines

Quick answer

Estimating project duration: sum the critical path (with buffers), not all tasks — parallel work doesn’t add; the longest chain sets the length.

The math

The critical path’s sum = project duration — parallel paths don’t add, they overlap.

Three-point durations

Expected = (O+4M+P)/6 per critical task — the range gives the range of finishes.

Adding buffer

Project buffer on the chain (critical chain style) — the schedule’s honest margin.

The sanity check

Comparable history — ‘how long did similar take?’ is the reality check the math needs.

Bottom line

Estimating project duration: sum the critical path (with buffers), not all tasks — parallel work doesn’t add; the longest chain sets the length.

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