Decompose scope, then sequence the work
Estimation That Survives Contact with Reality
Three-point estimates, story points, reference class forecasting and the planning fallacy.
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Humans are systematically optimistic about their own plans and reasonably accurate about other people's. Good estimation practice is mostly a set of tricks for exploiting that asymmetry.
Three-point (PERT)
Expected duration = (Optimistic + 4 × Most Likely + Pessimistic) ÷ 6, with standard deviation (P − O) ÷ 6. Report the range, never the single number — a point estimate quoted upward becomes a commitment by Friday.
Relative sizing
- Story points measure size and complexity, not hours. They work because relative comparison is more reliable than absolute prediction.
- Velocity is a forecasting input, not a performance metric. The moment it is used to compare teams, it inflates.
- Use throughput (items per week) when items are of similar size — it needs no estimation at all.
Related PMI standards & templates
External resources on pmi.org — links open in a new tab. Some require PMI membership.
PMI standard templates for this topic
Editable Word and print-ready PDF downloads — no sign-up required.
- Project plan pack template →A PMI standard project plan template pack: the nine-section plan document plus a schedule worksheet with duration, dependency, float and milestone tabs.
- Lessons learned log template →A PMI standard lessons learned log template with a facilitation walkthrough, a worked example and the review cadence that stops lessons being written from memory at closure.
- Sprint planning template →A PMI standard sprint planning template with a capacity calculator, a Definition of Ready check, a two-hour agenda and a worked example of a commitment that fits.
- User story template →A PMI standard user story template with Given/When/Then acceptance criteria, an INVEST check, a fully worked example and the six patterns for splitting a story that is too big.
The PM Delivery Toolkit turns everything in this guide into fill-in templates — $25, one payment.
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