What happens if I add a month to a date near the end of the month?

If adding months or years lands on a day that doesn't exist in the target month (like adding 1 month to 31 Jan), the result rolls over to the equivalent day count in the following month, so "31 Jan + 1 month" gives a date in early March rather than an invalid 31 Feb.

Can I go backward from a date without switching the operation?

Yes, choose "Subtract" as the operation and enter a positive amount, or you can leave it on "Add" and think of the amount as how far forward you want to move — both the add and subtract options use the same underlying date arithmetic.

Add or Subtract Dates Calculator

Add or subtract days, weeks, months or years from a date.

How this is calculated

Result date = Start date ± amount (days/weeks/months/years)

Assumptions used in this calculation

Calendar: Uses the Gregorian calendar; month and year arithmetic accounts for variable month lengths and leap years.

About this calculator

This calculator adds or subtracts a number of days, weeks, months or years from a starting date and shows the resulting date and day of the week.

Worked example

Add 30 days to 1 Jan 2026

Result: 31 Jan 2026

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Frequently asked questions

Date Difference Calculator

Find the number of days, weeks, months and years between two dates.

Working Days Calculator

Count working days between two dates, excluding weekends and holidays.

Add or Subtract Dates Calculator

About this calculator

Frequently asked questions

What happens if I add a month to a date near the end of the month?

Can I go backward from a date without switching the operation?

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