Date & Time
Add / Subtract Days Calculator
Calculate a date before or after a chosen number of days, weeks, months, or years.
Add / Subtract Days Calculator tool
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About This Tool
Use this date calculator to find the calendar date before or after a starting date. It supports whole-number day, week, month, and year intervals for deadlines, renewal dates, schedules, reminders, follow-ups, and planning checks. Month and year calculations follow real calendar boundaries, including leap years and month-end clamping, rather than treating every month as a fixed number of days.
How To Use It
- Choose the starting calendar date for the calculation.
- Enter a whole number and select days, weeks, months, or years.
- Choose whether the interval should be added to or subtracted from the start date.
- Review the resulting date, weekday, and date-input format.
- Check the rule you are following when a deadline counts the start date, excludes weekends, or treats the due date differently.
Examples
30 days from a date
Add 30 days to a start date to find the future calendar date for a reminder, deadline, or follow-up.
Two weeks before an event
Subtract 2 weeks from an event date to find when preparation should begin.
One month from January 31
Month additions clamp to the final valid day of the destination month.
One year from leap day
Adding 1 year to February 29, 2024 gives February 28, 2025 because 2025 does not have February 29.
Subtract across a year boundary
Subtracting 2 months from January 31, 2026 gives November 30, 2025 because November has only 30 days.
Useful Notes
Month-end behavior
If the destination month has fewer days, the result uses the last valid day of that month.
Calendar units
Weeks are treated as 7 calendar days. Months and years follow real calendar boundaries instead of fixed day counts.
Whole-number intervals
The calculator intentionally accepts whole numbers only. Fractions such as 1.5 months can be ambiguous because months have different lengths and calendar rules vary by context.
Calendar days, not business days
Adding 10 days counts every calendar date, including weekends and holidays. Use the Business Days Calculator when the schedule should skip weekends or entered holidays.
No timezone or daylight-saving adjustment
The calculation uses calendar dates only, not times of day or timezones. It does not adjust for daylight-saving transitions, travel between zones, or exact elapsed hours.
FAQ
Does January 31 plus one month become February 28?
Yes in a non-leap year. The calculator clamps to the final valid day instead of overflowing into March.
Can I enter decimals?
No. This calculator uses whole day, week, month, or year intervals so the resulting calendar date is unambiguous.
Does adding 7 days always equal adding 1 week?
Yes. Weeks are treated as exactly 7 calendar days in this calculator.
Are weekends and holidays skipped?
No. This tool adds or subtracts calendar units. Use the Business Days Calculator when weekends or holidays should be excluded.
Can I use this for legal or contractual deadlines?
Use it for the arithmetic, but verify the required counting rule. Some rules include the start date, exclude weekends or holidays, or move deadlines that fall on non-working days.