How would you communicate a delivery estimate when a vendor dependency has uncertain duration?

Instruction: Give the scenario dates, distinguish an estimate range from a confidence interval and identify what evidence would narrow it.

Context:

Fictional planning case: vendor approval must finish before a four-working-day build, followed by two working days of testing. Vendor approval may take 2, 5 or 10 working days in the scenarios supplied. No probabilities are available. Work begins on day 1, with no overlap between these stages. Leadership wants a commitment before the vendor responds.

Updated

Estimate and communication

Total duration is vendor approval plus six days: the scenarios finish at the end of working day 8, 11 or 16. I would present those as scenarios, not assign an invented 80% confidence or average probability. The five-day vendor assumption gives an 11-day planning target, but its likelihood is unknown.

Ask the vendor for its actual queue, prerequisites and written service expectations; review comparable approval history and whether our submission is complete. Time-box that investigation and give leadership a checkpoint for a firmer estimate. If a commitment is unavoidable, the sponsor must understand the chosen contingency and the residual risk.

Follow-up

Would adding developers solve the uncertainty? Not the predecessor approval delay. It may shorten later work only if engineering validates that the work is divisible. The useful distinction is what changes the dependency and what changes the downstream duration.

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