15 tools
Add & subtract
Move a date forwards or backwards by a span, with the calendar's rules applied. Each tool has its own page. It runs in your browser, and it keeps its inputs in the address bar so you can share the answer.
The tools
Add or take away days, weeks, months, years, hours, minutes or seconds. Month ends and leap days are handled, and each page explains the rule it uses.
Add Days to DateAdd any number of days to a date and get the answer with its weekday, plus the same date counted in working days for anything with a deadline attached.
Add Weeks to DateWeeks are the easy case — always seven days, always the same weekday. Add them and get the date, the weekday and the week number.
Add Months to DateMonths added on the calendar, with the end-of-month case handled explicitly — 31 January plus one month is 28 February, and the page says so rather than silently landing in March.
Add Years to DateYears added on the calendar, with 29 February clamped to the 28th in a common year, and the resulting weekday shown.
Add HoursHours added to an instant, with the date rollover shown, and a note when the span crosses a daylight-saving change and the clock does not move by what you added.
Add MinutesMinutes added to a time, with hour and date rollover handled, and the answer on the 24-hour clock.
Add SecondsSeconds added to an instant, with the resulting Unix timestamp beside the human reading — for anything you are about to put in a token or a cache header.
Subtract DaysDays taken off a date, with the weekday, and the working-day answer beside it for anything counted backwards from a deadline.
Subtract WeeksWhole weeks taken off a date — the weekday is guaranteed to be the same, which makes this the safest way to step backwards.
Subtract MonthsMonths taken off on the calendar, with the shorter-month case clamped and stated — and a warning that month arithmetic does not reverse cleanly.
Subtract YearsYears taken off a date, with leap-day clamping, the weekday, and the age that span would make someone.
Date Offset CalculatorOne field for the whole offset — `2y 3mo 10d`, `+6 weeks`, `-90 days` — applied in calendar order, with each step shown so you can see what happened.
Time Offset CalculatorHours, minutes and seconds applied to an instant, with the resulting timestamp, the date rollover, and any daylight-saving transition the span crossed.
Future Date CalculatorCount forward from today by any span and get the date, its weekday, its week number, and how many working days away it is.
Past Date CalculatorCount backwards from today by any span — days, weeks, months or years — and get the date with its weekday and week number.