PM Estimation
(2026 Edition)
Honest estimation means giving ranges instead of single points, using reference-class forecasting instead of gut feel, separating unknowns from knowns before committing a number, and buffering 30–50% for integration and review rather than padding for slack. It also means naming the biases that distort estimates — planning fallacy, sunk-cost thinking, optimism bias, and scope creep — since the first estimate is always wrong and gets re-estimated every sprint.
By Naman Goyal · Product manager · Builder of PM Streak · Updated July 3, 2026
5 estimation practices and 4 biases to catch yourself on.
Build Estimation PM Skills — Free →5 Practices
Estimate ranges, not points — '2–4 weeks' beats '3 weeks'
Reference-class forecasting — compare to similar past projects, not your optimism
Separate unknowns from knowns — list open questions before estimating
Buffer 30–50% for integration and review — not for slack
Re-estimate after every sprint — the first estimate is always wrong
4 Biases
Planning fallacy — we underestimate our own tasks by 30–50% consistently
Sunk-cost — already invested time inflates willingness to continue
Optimism bias — engineers and PMs both suffer, just in different ways
Scope creep — small additions silently extend timelines
FAQ
Why do engineering estimates slip so often?
Partly because we ignore integration, review, edge cases, and unknowns. Partly because the environment rewards optimistic estimates over realistic ones. The fix is systemic: reference-class forecasting, honest buffers, and rewarding truth-telling over short-term promises. Over a year, teams that estimate honestly ship more, not less.
Keep learning