Calculators › Add or subtract days calculator
Add or subtract days calculator
Enter a date and an amount — the resulting date, its weekday and ISO week number update instantly. Negative numbers subtract.
Calculator
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Resulting date
Weekday—
ISO week—
How it works
Days and weeks add on the day axis. Months and years add on the calendar: the month and year fields advance and the day-of-month is clamped to the target month's real length — so Jan 31 + 1 month = Feb 28 (or Feb 29 in a leap year), never an impossible date.
Frequently asked questions
What happens to Jan 31 plus one month?
February has no 31st, so the result clamps to the last real day of February — Feb 28, or Feb 29 in a leap year. This matches how legal and accounting due dates are usually computed.
How do I subtract?
Enter a negative amount, for example −14 days. The calculator handles any sign.
Is a year always 365 days here?
No — adding 1 year advances the calendar year, so it lands on the same month and day next year, automatically respecting leap years.