How to use

Shift a starting date forward or backward by years, months, weeks and days in one calculation. Month and year changes preserve the day when possible and clamp to the target month's final valid day when necessary.

Choose the start date and whether to add or subtract.
Enter any combination of non-negative whole years, months, weeks and days.
Calculate to see the resulting date, weekday and total calendar-day distance.

How it is calculated

Years and months are shifted first with the day clamped to the last valid day, then weeks × 7 and days are applied.

Example

Example: January 31, 2026 + 1 month = February 28, 2026 under the month-end clamping rule. Weeks and days are then applied after calendar months.

Important notes

This tool uses calendar days and does not exclude weekends or public holidays. Legal, contractual or business-day deadlines may use different inclusion rules, so confirm the governing rule for official obligations.

Frequently asked questions

What happens when I add one month to January 31?

If day 31 does not exist in the target month, the calculator uses that month's last valid day, such as February 28 or 29.

Are weekends counted?

Yes. This is calendar arithmetic, so Saturdays and Sundays count like other days.

Can I combine years, months and days?

Yes. Years are applied first, then months, then weeks and days so the rule is predictable.

Is this calculator free?

Yes. It is free to use and requires no account.

Date Add/Subtract Calculator