Add or subtract days, weeks, months or business days from a date

How to use the date calculator

1. Set the Start date. It is filled in with today’s date (the UTC date, which can differ from yours near midnight).
2. Choose Add or Subtract under Operation.
3. Type the Amount (whole numbers only) and choose the Unit: Calendar days, Business days, Weeks, Months or Years.
4. For Business days, choose which days are the Weekend and list any Holidays to skip (optional), one YYYY-MM-DD date per line.
5. The Result shows the full date with its weekday, plus the ISO date, the calendar days from the start, the ISO week and the day of the year.

What it does and when to use it

Use it for notice periods, return windows, visa stay limits, project milestones, or looking back to find when something started. The business-day unit answers questions such as “10 working days from Friday” for shipping times, payment terms or office deadlines. The weekend can be Saturday and Sunday, Friday and Saturday, Sunday only or Friday only, to match working weeks in different countries.

To count the days between two dates instead, use the date difference calculator or the business days calculator. For a live count to a single date, try the days until calculator.

How it works

Each date becomes a day number, counted from 1 January 1970 in the Gregorian calendar, using whole-number arithmetic. Days and weeks are added to that number directly (a week is 7 days). Months and years change the month count first and then clamp the day to the length of the target month. Business days step one day at a time and skip weekend days and your holidays. No clock time is involved, so every time zone gets the same result.

Worked examples

A 30-day notice period. Start 15 January 2027, add 30 calendar days: Sunday, 14 February 2027, day 45 of the year, ISO week 2027-W06.

Six months back from a month end. Start 31 August 2026, subtract 6 months: Saturday, 28 February 2026. February 2026 has no 31st, so the tool uses the last day and says so.

Working days over Christmas. Start Friday 18 December 2026, add 5 business days with 2026-12-25 and 2027-01-01 as holidays: Monday, 28 December 2026. The days counted are 21, 22, 23, 24 and 28 December, because Christmas Day and the weekend are skipped.

Limits and tips

• Results must fall between years 1 and 9999, and the amount must stay under 3,000,000.
• Holidays are used only with Business days. Lines that are not valid dates are listed in a warning and ignored.
• Dates before 1582 follow the modern Gregorian rules extended backwards, which differ from the Julian calendar used at the time.
• To check what weekday any date falls on, use the day of the week finder.