How to use it
- The start date is today when the page opens; change it to any date, or press Today to come back.
- Choose Add or Subtract.
- Type a whole number and choose days, weeks, months or years.
- Read the resulting date, its day of the week and the number of calendar days between the two dates.
How the date is calculated
- Days and weeks are added as calendar days (a week is 7 days). Weekends and holidays are included.
- Months move to the same day of the target month. When that month is shorter, the date becomes the month’s last day: 31 January + 1 month = 28 February 2026, and 31 March − 1 month = 28 February too.
- Years are 12 months, with the same rule: 29 February 2024 + 1 year = 28 February 2025.
The day count under the result tells you how long a “month” or “year” really was in days.
Worked example
Start date 3 November 2026, add 90 days:
- 27 days remain in November, then 31 in December and 31 in January: 89 days take us to 31 January;
- one more day gives Monday, 1 February 2027.
Example with months: 31 January 2026 + 1 month = 28 February 2026, which is 28 calendar days later.
Tips
- Deadlines such as “within 30 days” usually mean calendar days; “within 10 business days” means working days, which this tool does not skip.
- Pregnancy, warranties and notice periods are often counted in weeks or months; choose the unit the document uses, because 3 months and 90 days rarely land on the same date.
- To see how far apart two dates are, use the days between dates calculator.