Enter a base date, choose Add or Subtract, and enter years, months, weeks and days. The date and weekday update immediately. All four duration fields stay independent.
The order is years → months → weeks → days. Years and months are combined into a total month offset applied once to the original date. If its day does not exist in the target month, the last day is used. Then weeks × 7 + days is applied.
January 31, 2026 + 1 month is February 28; + 2 months is March 31. January 30, 2026 + 1 month + 3 days is March 3. October 13, 2026 + 30 days is Thursday, November 12, 2026.
February 29, 2024 + 1 year is February 28, 2025. May 31, 2026 − 1 month is April 30. Months are not traversed one at a time, so the original day is retained whenever the target month supports it.
An all-zero duration returns the base date. Calendar calculations are independent of time zones and DST and include weekends and holidays. Supported years are 0001–9999. Unsafe numbers or out-of-range dates show an explanation instead of a result.