How to use this calculator
- Pick the start date, or press "Today".
- Choose add or subtract.
- Type the years, months, weeks and days, or press a quick pick such as "30 days". Leave the rest empty.
- Read the new date, with its day of the week. Press "Copy" to copy it.
How it's calculated
Years and months are added first, keeping the same day of the month. If that day doesn't exist in the new month, we use the month's last day (31 January + 1 month = 28 February, or 29 in a leap year). Then the weeks and days are added, counting every calendar day. The start date itself isn't counted: 1 day after Monday is Tuesday.
Worked examples
When people use it
- Invoice due dates: an invoice dated 11 October 2026 on "Net 30" terms is due 30 days later, on 10 November 2026. Your contract may count differently, so check its wording.
- Notice periods and deadlines: "4 weeks from today" or "90 days before the renewal".
- Planning: how far ahead a date is, or which day of the week it falls on.
Frequently asked questions
Does it skip weekends and bank holidays?
No, it counts every calendar day. To add working days only, skipping weekends and US or UK public holidays, use our business days calculator.
Is "1 month" always the same as 30 days?
No. Months have 28 to 31 days, so adding 1 month keeps the day of the month (5 March → 5 April), while adding 30 days doesn't always. Use whichever your contract or rule says.
How far forward or back can I go?
Any date from the year 1 to 9999. Dates use today's calendar (the Gregorian calendar) all the way back, so very old historical dates may not match what was written at the time.