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A PM has a "business days between two dates" formula they've been carrying from spreadsheet to spreadsheet for years:
=SUMPRODUCT(--(WEEKDAY(ROW(INDIRECT(B2 & ":" & C2)), 2) < 6))
It works (mostly) but has three downsides: (1) it relies on INDIRECT which is volatile and recalcs on every change anywhere in the workbook; (2) it doesn't take a holiday list — the team has to subtract holidays manually; (3) reading it requires understanding ROW + INDIRECT + WEEKDAY-mode-2 + the boolean-to-number coercion. Hard to maintain; harder to explain.
NETWORKDAYS collapses this into a one-call formula:
=NETWORKDAYS(B2, C2)
NETWORKDAYS counts the weekdays between two dates inclusive of both endpoints, automatically skipping Saturdays and Sundays. The optional third argument is a holiday range; we don't have one for this problem, but it slots in cleanly when needed: NETWORKDAYS(B2, C2, $E$2:$E$10).
The data at B2:C13 has 12 project rows with start and end dates spanning roughly four weeks each.
Your task:
Graded cells: D2 (2026-01-05 → 2026-01-30 → 20), D5 (2026-04-06 → 2026-04-30 → 19), D10 (2026-09-07 → 2026-09-25 → 15).