date ± duration
add or subtract any combination of time from a date
- iso
- 2026-04-30T00:00:00.000Z
- weekday
- Thursday
- day of year
- 120
- unix
- 1777507200
── about this calculator ──
Date math is the small but constantly-needed task of asking "what date is N days/weeks/months from this one?" — and just as often "what date was N before it?" Use this calculator for project planning, due-date tracking (gestation, library books, warranties), tax and contract deadlines, prescription refill dates, vacation scheduling, and any kind of countdown that starts from a fixed point.
Each unit is added independently in a defined order: years, then months, then weeks and days together, then hours and minutes. This matches the natural human reading of "1 year, 2 months, 3 weeks from today". The result is shown in your browser's locale, but the breakdown also gives you ISO 8601, weekday name, day of year, and Unix timestamp for downstream use.
── frequently asked ──
- › How are months added when the source day doesn't exist in the target month?
- We follow the standard JavaScript Date behavior: adding one month to January 31st rolls over to March 3rd (because February doesn't have a 31st). If you need a strict 'last day of next month' result, subtract a day after adding.
- › Why does adding 'years' sometimes shift by a day?
- Leap years. Adding one year to February 29th lands on March 1st of the following non-leap year because there is no Feb 29th to land on.
- › What is 'day of year' in the result?
- An integer from 1 to 366 representing the position of the result date in its calendar year. January 1st is day 1; December 31st is day 365 (or 366 in a leap year).
- › What is the 'unix' value?
- The number of seconds elapsed between January 1, 1970 UTC and the result date. It's the standard timestamp format for databases, APIs, and most programming languages.