How do you calculate project milestone delay?

Question

Sheet Reserve · Accepted Answer

Subtract the baseline milestone date from the current finish date. Use the actual completion date once completed and the current forecast while incomplete. A baseline of October 10 and forecast of October 15 gives a five-day delay. Negative values mean earlier than baseline. Keep baseline, forecast, and actual dates separate so the comparison remains reproducible.

With baseline C11, forecast D11, and actual E11, current finish is =IF(E11="",D11,E11). Subtract baseline from that result when both dates are populated.
Does this milestone formula count working days?
No. Direct date subtraction counts calendar days. Working-day schedules need an explicit weekend pattern and holiday calendar rather than an assumption hidden in the formula.