Plain DatesClear date calculations, with the rules shown.

Date addition calculator

Add or subtract from a date

Move a calendar date by a number of days, weeks, months, or years. Month and year calculations preserve the day when possible and use the last valid day when it is not.

Calculate a new date

Use a positive or negative whole number.

Days and weeks versus months and years

Adding seven days and adding one week produce the same result. Months and years are different because their lengths vary. This calculator changes the calendar month or year first, then checks whether the original day exists in the destination.

If it does not, the result is clamped to that month’s last day. January 31, 2025 plus one month is February 28, 2025. In a leap year, January 31, 2024 plus one month is February 29.

Leap-day example

February 29, 2024 plus one year is February 28, 2025. Subtracting one year from February 29 follows the same last-valid-day rule.

When another rule may apply

This result is ordinary calendar arithmetic. A contract, court, workplace, school, or government agency may use a different rule when a target date falls on a weekend or holiday. Use the rule published for that specific deadline rather than treating this calculator as legal guidance.

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