Add business days while skipping weekends

“Three business days after Friday” is not three calendar days after Friday. This example defines business days as Monday through Friday, advances one timedelta(days=1) at a time, and decrements the remaining count only when date.weekday() is below 5. Starting on Friday 2026-05-01, it visits Saturday and Sunday without counting them, then counts Monday, Tuesday, and Wednesday. The returned date is 2026-05-06.

The function deliberately accepts only non-negative counts. Its zero case returns the starting date because the loop does not run. That choice should be stated in a caller’s contract: some systems instead define “zero business days” as the next business day when the input is a weekend. The assertions show the selected convention for this one Friday input and do not prove correctness for every calendar.

Weekends are not a complete business calendar. This code neither knows public holidays nor short working days, regional weekends, closures, or deadlines with times of day. Add those rules from a maintained, jurisdiction-specific source if they matter. The example uses only date, timedelta, and date.weekday() from Python’s standard library and works on Python 3.2+.

The Python datetime documentation defines date arithmetic and documents that weekday() maps Monday to 0 and Sunday to 6.

AI-assistance disclosure: This article was drafted with AI assistance and should be reviewed in its application context.

from datetime import date, timedelta


def add_business_days(start, count):
    if count < 0:
        raise ValueError("count must be non-negative")

    current = start
    remaining = count
    while remaining:
        current += timedelta(days=1)
        if current.weekday() < 5:
            remaining -= 1
    return current

arrival = add_business_days(date(2026, 5, 1), 3)

assert arrival == date(2026, 5, 6)
assert arrival.weekday() == 2

print(arrival.isoformat())
2026-05-06

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