How to use
- Enter the start date. It begins as today.
- Choose Add for a later date or Subtract for an earlier one.
- Enter any mix of years, months, weeks and days, or tap a quick pick.
- Read the new date, its weekday and its week number.
How the date is calculated
step 1: start ± (years × 12 + months), kept within the month
step 2: result ± (weeks × 7 + days)
- Months first. Years and months are added together. If that day doesn’t exist, the date moves to the last day of the month: 31 January + 1 month = 28 February (29 in a leap year).
- Then days. Weeks and days are plain calendar days, so weekends and holidays count.
Examples
- 90 days after Wednesday, 21 October 2026 is Tuesday, 19 January 2027.
- 30 days before 21 October 2026 was Monday, 21 September 2026.
- 31 January 2026 + 1 month is 28 February 2026.
- 29 February 2024 + 1 year is 28 February 2025.
Days from 21 October 2026
| Add | Date | Weekday |
|---|---|---|
| 30 days | 20 November 2026 | Friday |
| 60 days | 20 December 2026 | Sunday |
| 90 days | 19 January 2027 | Tuesday |
| 100 days | 29 January 2027 | Friday |
| 180 days | 19 April 2027 | Monday |
| 6 months | 21 April 2027 | Wednesday |
| 1 year | 21 October 2027 | Thursday |
Why the order matters
Adding months before days gives a different answer from adding days first. 30 January 2026 + 1 month is 28 February, then + 1 day is 1 March 2026. Adding the day first would give 28 February.
Month steps are not always reversible. 31 March − 1 month = 28 February, but 28 February + 1 month = 28 March.
Contracts sometimes define a “month” differently, so check the wording for legal deadlines.
To skip weekends and holidays, use the business days calculator. To count the days between two dates, use the days between dates calculator.