How to use the Add or Subtract Days
- Choose the start date.
- Choose add or subtract and enter the number of days.
- Press Calculate.
Formula
Each day is exactly one calendar day, so month lengths and leap years are handled automatically.
Examples
- 90 days after 26 October 2026 is Sunday 24 January 2027.
Frequently asked questions
Does day 1 start today?
Adding 1 day to today gives tomorrow. If your rule says “within 30 days including today”, add 29.