Date before N days
Find the date N days before a start date in UTC calendar days. Example: 2025-03-31 minus 100 days is 2024-12-21. The result is a YYYY-MM-DD date.
What to know
This page works backwards from a Start date. Type a whole number in the Days field and the result is the earlier calendar date, formatted YYYY-MM-DD, using start - N x 86,400,000 ms on UTC midnight.
Think of it as planning from a deadline. If a filing is due on 2025-03-31 and the preparation needs 100 days, the work must begin on 2024-12-21. A 14-day notice before 2025-03-01 lands on 2025-02-15, and 30 days before 2025-03-01 is 2025-01-30.
Year boundaries and leap days are handled by the calendar. Subtracting 365 days from 2025-03-01 gives 2024-03-01, while subtracting 365 days from 2024-03-01 gives 2023-03-02 because the span contains 29 February 2024.
The Days field accepts whole numbers of 0 or more, and 0 returns the start date unchanged. The start date is not counted as a day, so one day before 2025-03-01 is 2025-02-28 and not the 1st.
Common backward-planning jobs are the start of a notice period, the last day to order for a delivery date, the cutoff for a refund window and the date a document must be requested. Subtracting 7 returns the same weekday one week earlier, which makes weekly schedules easy to roll back.
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How to use Date before N days
- Enter Start date 2025-03-31, the deadline.
- Type 100 in the Days field.
- Read the Result line, which shows 2024-12-21.
- Try 14 in Days to see a two-week lead time on 2025-03-17.
Quick answers
What date is 30 days before 2025-03-01?
It is 2025-01-30, since February 2025 has 28 days and the count reaches back into January.
Is the start date included in the N days?
No. The start date is day zero, so 1 day before 2025-03-01 is 2025-02-28 and the result moves one calendar date per day.
Can I subtract working days only?
Not on this page. It removes calendar days without skipping weekends or holidays.