Date Add or Subtract Calculator
Add or subtract days, weeks, months and years from any date — in calendar days or business days that skip weekends and US, Mexican or Spanish holidays — and see the exact date, weekday and a repeating schedule.
How it works
result = start ± (years·12 + months) on the calendar, then ± weeks·7 days, then ± days (calendar days, or business days that skip weekends and holidays)
Years and months are applied on the calendar first: the date moves to the same day number in the target month, and is pulled back to the last day when that month is shorter (one month after January 31 is the end of February). Weeks are then added as seven calendar days each. In calendar-day mode the days are added the same way, so every weekend, holiday and leap day counts. In business-day mode the calculator walks one day at a time from the date it has reached and only counts days that are not weekend days or chosen holidays, so one business day after a Friday is the following Monday. You can change which days are the weekend, skip US federal holidays (with their Friday/Monday observed dates), Mexico’s official rest days or Spain’s national holidays, count the start date as day 1 for “including today” terms, and repeat the offset to build a schedule.
Worked example
From Thursday, October 1, 2026, add 15 business days with a Saturday–Sunday weekend: the count runs Friday Oct 2 (1), Oct 5–9 (2–6), Oct 12–16 (7–11) and Oct 19–22 (12–15), landing on Thursday, October 22, 2026 after skipping 6 weekend days. Adding 15 calendar days instead lands on Friday, October 16, 2026. With US federal holidays on, Columbus Day (Monday, October 12) is skipped too, so the 15th business day becomes Friday, October 23, 2026.
Sources: OPM — Federal holidays · Mexico — Federal Labor Law, Article 74
Frequently asked questions
Why does adding one month sometimes not keep the day number?
When the target month is shorter than the start day, the date stops on the last valid day. One month after January 31 is February 28 (29 in a leap year), because there is no February 31.
How are business days counted?
The start date itself is never counted. From the next day on, each weekday that is not a chosen holiday counts as one business day, so 1 business day after Friday is Monday and 5 business days after a Monday is the next Monday.
What does “count the start date as day 1” do?
Some contracts and prescriptions count the first day as day 1, so a 30-day period that starts on June 1 ends on June 30, not July 1. The toggle moves the result one day toward the start to match that convention.
Which holidays are included?
US federal holidays (with Saturday holidays observed on Friday and Sunday ones on Monday), Mexico’s official rest days from Article 74 of the Federal Labor Law, or Spain’s national holidays including Good Friday. Regional, state and company holidays are not included.
In what order are the fields applied?
Years and months first on the calendar, then weeks as 7-day blocks, then days. Doing the month step first keeps the day number stable before the fixed day offset moves it.
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This calculator is for educational purposes. Double-check important results before acting on them.