Add or Subtract Days from a Date
Add or subtract days, weeks, months or years from any date and get the day of the week
How to Use
- Pick the Start date. It is set to today when the page opens.
- Choose Add to go forward in time or Subtract to go back.
- Enter any mix of years, months, weeks and days, for example 0 years, 6 months, 0 weeks, 15 days.
- The new date appears as you type, with its day of the week, day of the year and week number.
- If the start day doesn't exist in the target month (such as 31 January + 1 month), a note explains that the last day of the month was used.
What this calculator does
It answers questions like "what date is 90 days from today?", "what was the date 6 months ago?" or "when does a 1 year 3 month course end?". Common uses in India include notice periods, the 45-day or 90-day windows on bills and returns, warranty and insurance expiry dates, EMI due dates, visa stays and medicine courses.
How the date is worked out
Years and months are added first, then weeks and days:
2. If the day doesn't exist in that month, use the month's last day
3. Add (weeks × 7 + days) calendar days
Step 2 is called clamping. Months have 28 to 31 days, so "one month after 31 January" has no exact answer. The usual convention, followed by spreadsheets and most programming libraries, is to stop at the last valid day: 28 February, or 29 February in a leap year. One month after 31 May is 30 June. For subtraction, 31 March minus 1 month is 28 (or 29) February.
The order matters. 31 January + 1 month + 1 day is 1 March (28 Feb + 1 day). Adding the day first would give 1 February + 1 month = 1 March as well. With other dates, such as 30 January, the two orders can differ by a day.
Worked examples
| Start | Change | Result |
|---|---|---|
| 12 Oct 2026 (Mon) | + 30 days | 11 Nov 2026 (Wed) |
| 12 Oct 2026 | + 90 days | 10 Jan 2027 (Sun) |
| 12 Oct 2026 | − 100 days | 4 Jul 2026 (Sat) |
| 31 Jan 2028 | + 1 month | 29 Feb 2028 (leap year) |
| 29 Feb 2024 | + 1 year | 28 Feb 2025 |
| 12 Oct 2026 | + 1 year 2 months 3 weeks 4 days | 6 Jan 2028 (Thu) |
Leap years, day of year and week number
A year is a leap year if it divides by 4, except century years, which must divide by 400. So 2028 is a leap year, 2100 is not, and 2000 was. The day of the year counts from 1 on 1 January to 365 (or 366) on 31 December; 12 October 2026 is day 285. The week number follows ISO 8601, used in Europe and many company calendars. Weeks start on Monday, and week 1 is the week that contains the year's first Thursday. So 1 January 2027 falls in week 53 of 2026.
Counting tips
- "Within 30 days of" usually means up to and including day 30 after the event. Check the exact wording of a law or contract. Some count the starting day and some don't.
- For deadlines that skip weekends and holidays, use a working-days calculator instead of adding calendar days.
- This calculator uses the Gregorian calendar for all dates, including those before 1582.