Add or subtract years, months, weeks, and days from a date and see the resulting date and its weekday.
| ISO date | – |
| Day of the week | – |
| Calendar days from start | – |
| Day of the year | – |
| Leap year | – |
| Step | Applied | Date |
|---|
| Days | Before | After |
|---|
The Date Calculator answers 'what date is 30 days from now', '6 months before this date', or '18 years and 3 months after that one'. Enter a start date, choose add or subtract, fill in any mix of years, months, weeks, and days, and the result appears with its weekday. A table of common offsets (7, 14, 30, 45, 60, 90, 180, and 365 days before and after) covers deadlines, payment terms, return windows, and probation periods at a glance. It is meant for anyone scheduling around a fixed date: contract dates, medication courses, notice periods, warranty ends, or travel plans.
The start date is parsed as a local calendar date at midnight. Years and months are applied first as calendar units: the month number is shifted and, if the original day of the month does not exist in the target month, the result is clamped to the last day of that month, so Jan 31 plus 1 month is Feb 28 (Feb 29 in a leap year) and Feb 29 plus 1 year is Feb 28. Weeks are converted to 7 days each and added together with the days last, using the JavaScript Date setDate method, which rolls across month and year boundaries and is unaffected by daylight-saving changes because everything stays at local midnight.
Feb 28, or Feb 29 in a leap year. There is no Feb 31, so the calculator clamps to the last day of February rather than rolling into March. This is the convention used by most calendar software and by rules such as 'due one month after the invoice date'.
Calendar months have different lengths, so adding 1 month then 1 day can differ from 1 day then 1 month. This tool applies years and months first, then weeks and days, which is the usual reading of a phrase like 'one month and one day from today'.
Enter the later date as the start date, switch the operation to Subtract, and enter 90 in the days field. The quick-offset table also shows 90 days before and after any start date without changing the inputs.
Feb 28 (Feb 29 in a leap year). Subtracting a month moves to the previous month and clamps the day, so Mar 31 minus 1 month is the last day of February. Rolling forward into March would be a different rule that this tool does not use.
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