How this calculator works
Years and months are combined and applied first. If the original day does not exist in the target month, it is clamped to that month’s final day. Weeks and days are then added or subtracted. This order is fixed and may differ from adding each component separately. Results are limited to 1900–2100.
The formula
Target = clamp(start shifted by years × 12 + months), then shift by weeks × 7 + days.
Subtract mode reverses both shifts.A quick example
31 January 2024 plus 1 month becomes 29 February 2024. Adding 1 month and 1 day in the same calculation gives 1 March 2024.
How to use this calculator
- Enter a starting date and choose Add or Subtract.
- Enter non-negative whole years, months, weeks and days.
- Calculate the new date and weekday.
A few common questions
What happens to 31 January plus one month?
It becomes the final day of February, rather than overflowing into March.
Is adding then subtracting a month always reversible?
No. Clamping may lose the original day, such as moving from a 31st to a shorter month.
Does this skip weekends?
No. Weeks are seven calendar days and no holidays or working-day rules are applied.