Date Calculator — Add or Subtract Days, Weeks, Months
Add or subtract years, months, weeks and days from any date, or count business days that skip weekends and your holidays, with weekday and ISO week.
This date calculator moves a date forward or backward by any mix of years, months, weeks and days, and tells you the weekday and ISO week of the result. Switch on business days to count working days only — useful for notice periods, payment terms ("net 30 business days"), shipping estimates and filing deadlines that skip weekends and public holidays.
How to use this tool
- Pick the start date (it defaults to today).
- Choose Add or Subtract and enter years, months, weeks and days — leave any of them at 0.
- For working days, tick the business-days box and, if needed, paste your holiday dates one per line.
- Read the resulting date, its weekday, the number of calendar days moved and the ISO week number.
Formula
Result = start + years × 12 months + months, then + weeks × 7 days, then + days (calendar or business)
Months are added on the calendar, not as 30 days: 15 March + 1 month is 15 April. If the day does not exist in the target month the result is the last day of that month, so 31 January + 1 month is 28 February (29 in a leap year). In business-day mode the start date is not counted; the calculator steps one day at a time and skips Saturdays, Sundays and every date in your holiday list.
Example
Starting on Thursday 24 December 2026, add 2 business days with 25 December listed as a holiday. Friday the 25th is skipped, the weekend is skipped, Monday 28 December is business day 1 and Tuesday 29 December 2026 is business day 2 — five calendar days after the start.
Frequently asked questions
Is adding 1 month the same as adding 30 days?
No. One month keeps the same day number (10 May → 10 June), while 30 days lands on a different day depending on the month's length. Use the Days field when a contract counts days.
Does the business-day count include the start date?
No. Counting starts the next day, which is how "within 5 business days" deadlines are normally read. If your rule counts the start day, subtract one.
Which holidays are skipped?
Only the dates you list, so the calculator works for any country or company calendar. For US federal holidays in a range, see the business days calculator.
What is the ISO week number?
ISO 8601 weeks start on Monday and week 1 is the week containing the year's first Thursday, so 1 January can belong to the previous year's week 52 or 53.
Last updated:
Page address with these inputs: https://kakao.mobile/tools/date-calculator/
Cite or embed this tool
kakaoCalc. (2026, November 8). Date Calculator — Add or Subtract Days, Weeks, Months. https://kakao.mobile/tools/date-calculator/
“Date Calculator — Add or Subtract Days, Weeks, Months.” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/date-calculator/.
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