➕ Date Add / Subtract Calculator
"What date is 90 days from today?", pick a start date, add or subtract days, weeks, months or years, and see the result with its weekday.
90 days after September 2, 2026 is
Tuesday, December 1, 2026
Months clamp to month-end: 31 Jan + 1 month = last day of February.
How the date add / subtract calculator works
Days and weeks are exact arithmetic. Months and years follow the calendar convention: the day-of-month is preserved where possible and clamped to the month's end where not, 31 January + 1 month gives 28 (or 29) February, not 2 or 3 March. That matches how billing cycles, notice periods and subscriptions roll dates. Order matters too: the tool applies whole years and months first (with that clamping), then adds or subtracts the exact number of days, so a mixed span like "1 year 2 months 10 days" resolves the calendar parts before the day count. The result also shows the day of the week it lands on.
The month-clamping rule is where hand-counting goes wrong most: "three months from 30 November" is 28 February, not 2 March. Deadlines defined in days (e.g. "within 30 days") and in months ("one month's notice") can differ by a day or three, check which your contract actually says.
Frequently asked questions
What does adding a month to 31 January give?
The last day of February, the 28th or 29th. The convention preserves the day-of-month and clamps to the target month's end when it doesn't exist, which is how billing and legal date rolls work.
How do I subtract days instead of adding?
Switch the direction toggle to "before", the same arithmetic runs backwards, e.g. 45 days before a deadline for a reminder date.
Is "30 days" the same as "one month"?
No, months are 28 to 31 days long, so a 30-day deadline and a one-month deadline diverge for most start dates. Use the unit your document specifies.
Does the result account for leap years?
Yes, the browser's calendar arithmetic knows every leap day. Adding one year to 29 February 2024 clamps to 28 February 2025.
What date is 90 days from today?
Set the start to today, add 90 days, and read off the result, for a mid-year start that's roughly three months ahead, though not exactly, since 90 days spans months of different lengths. Day-based deadlines like "within 90 days" are counted in exact days, which is what this mode gives, rather than in calendar months.
Should I count in days or in months for a deadline?
Use whichever unit the source specifies, because they diverge. "30 days" is always exactly 30 days, but "one month" is 28-31 depending on the start date, so the two can land days apart. Contracts, notice periods and warranties often hinge on this distinction, the tool handles both units separately so you can match the wording.
Does this run locally?
Yes, pure calendar arithmetic in your browser; nothing is sent anywhere.