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Date Add / Subtract

Add or subtract days, weeks, months or years from a date.

Runs in your browser — files never leave your device

Result date
2024-01-01

Use negative numbers to subtract.

How it works

Pick a start date, enter how far to move in years, months, weeks, and days — any mix, each with its own sign — and the tool returns the resulting calendar date in ISO YYYY-MM-DD form, recalculated on every keystroke. It answers everyday scheduling questions in both directions: 45 days after March 15, 2026 for a net-45 invoice is 2026-04-29, and 90 days before July 1, 2026 for a notice period is 2026-04-02.

Units apply in a fixed order: years first, then months, then weeks and days together, with every week counted as exactly 7 days. Starting from 2026-01-15 and adding 1 month plus 2 weeks, the tool first moves to 2026-02-15, then adds 14 days to land on 2026-03-01. Because month lengths vary from 28 to 31 days, the fixed order is what keeps results deterministic — the same inputs always produce the same date.

Month and year steps follow an overflow rule rather than clamping. When the target month is too short for the day you started on, the extra days roll forward into the next month: 2024-01-31 plus one month aims at the nonexistent February 31 and resolves to 2024-03-02 (February 2024 has 29 days; the remaining two spill into March), while the same addition from 2025-01-31 gives 2025-03-03 because February 2025 has only 28. Leap-day arithmetic follows the same rule: 2024-02-29 plus one year resolves to 2025-03-01, since February 29, 2025 doesn’t exist.

All arithmetic runs on pure calendar dates in UTC with no clock component, so time zones and daylight-saving transitions can never shift the answer by a day. Day and week additions are exact counts through real month lengths and leap years, which makes the tool reliable for contract deadlines, notice periods, visa and warranty windows, medication and follow-up schedules, sprint planning, and any “what date is N days from X” question you’d rather not count on your fingers.

Frequently asked questions

Why does January 31 plus one month give March 2 or 3 instead of February 28?
Because this calculator lets day-of-month overflow roll forward instead of clamping to the end of the month. 2024-01-31 plus one month targets “February 31”, and since February 2024 has 29 days, the two extra days spill into March, giving 2024-03-02; from 2025-01-31 the result is 2025-03-03 because February 2025 has only 28 days. Tools that clamp return February 28 or 29 instead — neither convention is wrong, but this one never silently shortens the day-of-month you entered.
In what order are years, months, weeks, and days applied?
Years first, then months, then weeks and days together, with each week counted as exactly 7 days. From 2026-01-15, adding 1 month and 2 weeks first moves to 2026-02-15 and then 14 days further to 2026-03-01. The fixed order matters because month lengths differ — it guarantees the same inputs always produce the same result.
How are leap years handled?
The math runs on the real Gregorian calendar, so February 29 exists only in leap years and day counts pass through actual month lengths. Adding 1 year to 2024-02-29 targets the nonexistent February 29, 2025 and rolls forward to 2025-03-01. Day arithmetic is always exact: 45 days after 2026-03-15 is 2026-04-29.
Can I add and subtract in the same calculation?
Yes — every field carries its own sign, so you can add months while subtracting days in one go, and the fixed order (years, months, then weeks and days) still applies. From 2026-01-15, adding 2 months and 10 days gives 2026-03-25; pure subtraction works the same way with negatives — 90 days before 2026-07-01 is 2026-04-02.
Do weekends, business days, or holidays factor in?
No — the tool counts calendar days, so weekends and public holidays are included in the span. 45 days after 2026-03-15 lands on 2026-04-29 no matter how many working days that covers. For business-day deadlines, compute the calendar date here, then check it against your jurisdiction’s holiday calendar.
Does my time zone or daylight saving time affect the result?
No. Inputs are treated as pure calendar dates in UTC with no clock time attached, so DST transitions and regional time zones can never shift the result by a day. The same inputs give the same date on any device, anywhere.
Are the dates I enter uploaded anywhere?
No — the calculation runs entirely in your browser. Nothing you type is uploaded, logged, or stored.

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