Give a range with the assumptions and unknowns attached, never a single date pulled out of the air. Break the work down enough to find the genuinely uncertain parts, spike those first, and commit to a firm date only once the biggest unknowns are resolved. State your confidence explicitly, reforecast as you learn, and keep the estimate (engineering judgment) separate from the commitment (a business decision).
Why interviewers ask this
Interviewers know estimation is where managers either build or destroy credibility. They want ranges over false precision, identification of the real unknowns, spikes to reduce uncertainty, and the discipline to update forecasts in public. The distinction between an estimate and a commitment is the detail experienced managers offer, because it is what stops a rough number becoming a marketing date overnight.
How to structure your answer
- Refuse a single number, and explain why in stakeholder friendly terms.
- Decompose to find the parts you genuinely cannot predict.
- Propose spikes that convert unknowns into estimates.
- Separate estimate from commitment and set a reforecast cadence.
Example answer
I never give one number to a question that big, but I also never say it depends and stop there, because that just sounds evasive. I give a range with reasons: eight to fourteen weeks, and the spread is driven by two things, whether the payments provider supports partial refunds natively and how much of the legacy import we have to keep working. Then I say what narrows the range: two days of spikes on those two questions and I will come back with something much tighter. That framing works because it turns waiting into a specific, short cost. I am also careful with the language of estimate versus commitment. An estimate is engineering judgment; a commitment is a business decision somebody makes holding that estimate, usually with buffer. On the last program I ran we reforecast every two weeks in public, the date moved twice, both times early, and because it was never a surprise nobody lost trust. The dates that wreck relationships are the ones that sit at green and then slip four weeks in one go.
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See how it worksFollow-up questions to expect
- How do you build in buffer without padding every estimate?
- What do you do when sales has already promised a date?
- How do you handle an estimate for work with a hard external deadline?
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