Date Calculator (Add or Subtract Days)
This calculator adds or subtracts a span of time from a date — “what date is 45 days from now”, or “what date was 90 days before Christmas”. Enter any mix of years, months, weeks and days, choose add or subtract, and get the resulting date, its weekday and the exact day count between the two dates.
How to use the date calculator (add or subtract days)
- Enter the start date.
- Choose whether to add or subtract, and fill in any combination of years, months, weeks and days (leave the rest at 0).
- Read the resulting date and the weekday it falls on.
Formula
Years and months are added first. When a month has no matching day (adding 1 month to 31 January, for instance, since February never has 31 days), the result is clamped to the last day of the target month rather than spilling into the month after. Weeks and days are then added on top of that.
Worked examples
Adding days
45 days after 1 October 2026 is Sunday, 15 November 2026.
The month-end edge case
Adding 1 month to 31 January 2026 gives Saturday, 28 February 2026 — not 3 March — because February 2026 only has 28 days.
Subtracting
90 days before 25 December 2026 is Saturday, 26 September 2026.
Why calendar math needs clamping, not just addition
The core problem
“Add one month” sounds simple until the start date is the 29th, 30th or 31st of a month, and the target month is shorter. There is no 31 April, no 30 or 31 February, and no 29 February outside a leap year. Something has to give, and different software handles it differently — some roll over into the following month (31 January + 1 month becomes 3 March), others clamp to the last valid day (28 or 29 February). This calculator always clamps, because rolling over silently changes which month you land in, which is rarely what anyone intends when they say “next month”.
Order of operations
Years are added first, then months (with clamping applied at that point), then weeks and days. This matters when combining units: adding 1 year and 1 month to 29 February 2024 adds the year first (landing on the clamped 28 February 2025), then the month.
Everyday uses
- Finding a deadline “60 days from today”.
- Working out a return date “2 weeks from departure”.
- Checking a renewal or expiry date “1 year after signing”.
- Finding a date a fixed number of days before an event, such as a shipping cut-off.
Practice problems
Try these yourself first, then check your answer. The answers come from the calculator above.
- What date is 6 months after 30 April 2026?
Show answer
Result: Friday, October 30, 2026
- What date is 2 weeks before 25 December 2026?
Show answer
Result: Friday, December 11, 2026
Common mistakes to avoid
- Expecting “31 January + 1 month” to land on the 31st of February, which does not exist; the result is clamped to the last real day of February instead.
- Entering the amount to subtract as a negative number as well as choosing “Subtract” — the two cancel out. Enter a positive amount and let the operation choose the direction.
- Forgetting that “weeks” and “days” both move by whole days, while “months” and “years” move by calendar units that can land on a shorter month.
Frequently asked questions
How do I find the date 30 days from today?
Enter today’s date, choose Add, and put 30 in the days field.
What happens if I add a month to the 31st of a month?
The result is clamped to the last day of the target month — for example 31 January + 1 month = 28 or 29 February, depending on whether it is a leap year.
Can I add and subtract at the same time?
Pick one operation per calculation. To mix (add 2 months but subtract 3 days), run the tool twice, once for each part.
How is this different from the days-between calculator?
This tool starts from one date and a span, and finds the other date. The days between dates calculator starts from two dates and finds the span.
Reviewed September 26, 2026 by the SolveCalcPro editorial team. Found a mistake? Tell us; see our editorial policy.