How this calculator works
Thirty days is a common notice period, challenge length and rough stand-in for a month. The calculator adds or subtracts exactly thirty calendar days, so the answer does not change just because the span crosses a short February or a 31-day month. The weekdays-inside figure counts Monday to Friday days after the start date through the result, which is a useful first estimate of the working days involved before holidays are considered.
Formula
result = fromOrdinal(O(start date) + 30) for a forward count, or fromOrdinal(O(start date) - 30) for a backward count. Weekdays inside = Monday to Friday dates in the half-open interval from just after the earlier date to the later date.
Worked example
30 days after 2026-11-01 is 2026-12-01, a Tuesday. The span is 4 weeks and 2 days with 22 weekdays inside. 30 days before 2026-11-01 is 2026-10-02, a Friday.
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Frequently asked questions
Is 30 days the same as one month?
Only approximately. Calendar months run from 28 to 31 days, so 30 days lands a day or two before the same date next month in some cases and a day after in others. Use the 6 month calculator or the month counter when the contract says a month rather than thirty days.
Does the start date count as day one?
By default no: the start date is day zero and the next date is day one. Choose the include option to make the start date day one, which moves the result one day earlier.
What is a 30-day notice period?
It is a requirement to give at least thirty calendar days of notice, usually counted from the day after the notice is given. Notice periods can be set by a contract or a statute, so check which days count and whether holidays extend the period.