Add or Subtract Days from a Date

Enter a start date, the number of days and whether to add or subtract. The calculator returns the resulting calendar date and its weekday, so you can check a deadline, a cooling-off period or a return window without opening a spreadsheet.

Every calculation runs in your browser. The dates, times and hours you enter are never sent to a server, saved to a cookie or stored in your browser.

Calculate

Result

Choose a start date, enter a number of days and select Calculate.

Typical uses

Setting a deadline

A task has a 14-day or 90-day limit. Add the number of days to the start date and you have the final date, including the correct weekday for scheduling.

Working with return and cancellation windows

If a return window is "30 days from delivery", subtract nothing and add 30 to the delivery date. The result is the last day on which the window is open.

Checking a date in the past

Use the subtract mode to go back by a number of days — for example, to find the date of a payment that fell 45 days before an invoice date.

Skipping across month ends

Adding 30 days is not the same as adding one month. The calculator keeps day arithmetic exact, so adding to 31 January or 29 February produces the real resulting date.

How adding and subtracting works

Both fields start from the same calendar date. Adding a positive number of days moves the date forward; choosing subtract moves it backwards.
Day arithmetic ignores months and years: adding 30 days always adds exactly 30 calendar days, whatever the month lengths in between.
Leap days are handled from the Gregorian calendar. Adding one day to 28 February 2024 gives 29 February 2024; in 2023 it gives 1 March.
Zero days is allowed and leaves the date unchanged, which is a quick way to look up the weekday of a date.
The resulting date always stays a real calendar date: month-end and year-end rollovers are normal, so 31 December plus one day lands on 1 January of the following year.
The weekday is derived from the same calendar arithmetic, never from the device clock or the user’s time zone.

How the result is calculated

The start date is converted to a whole-day index on the proleptic Gregorian calendar, the signed number of days is added to that index, and the result is converted back to a date. Working in whole days means month lengths, leap days and year boundaries are already part of the arithmetic instead of being special cases.

Limits and caveats

Only whole days can be added or subtracted. The calculator does not accept hours, minutes or fractional days.
Working days, holidays and weekends are not skipped. If you need the next working day, apply your own calendar rules.
Dates far outside the range a JavaScript date value can represent are rejected instead of being rounded.
The result is a date, not a deadline with a time of day: it cannot say whether something is due at the start or the end of that date.

Privacy and your data

Everything is computed locally in your browser. The start date and day count you enter are not transmitted, logged or saved, so the page can be used for private scheduling without leaving a trace.

These utilities are informational tools, not legal, payroll or tax advice. Check your contract or the rules that apply to you before relying on a result for a binding decision.

Frequently asked questions

What date is 30 days from today?: Enter today as the start date, choose add and enter 30. The calculator shows the exact date 30 calendar days later, with its weekday. If you meant one month rather than 30 days, note that the two are often a day or two apart.
Can I subtract days as well as add them?: Yes. Choose subtract and the same number of days is taken away from the start date, which is useful for deadlines that count backwards from an important date.
Does adding days change the weekday correctly?: Yes. The weekday is part of the same calendar arithmetic, so adding seven days always lands on the same weekday and the day-of-week stays consistent across month and year boundaries.
What happens at a month end?: The result is a real calendar date. Adding one day to 31 January gives 1 February; adding 30 days to 31 January gives 1 March in a non-leap year, because the count is exact days rather than a nominal month.

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