What happens at month end?

The day is clamped to the final valid day of the destination month.

Can values be negative?

Yes, although the Add/Subtract choice is clearer for most uses.

Date Add/Subtract Calculator

Add or subtract calendar time from a date.

Choose a start date.

What this calculator does

Add or subtract years, months, weeks, and days while handling month lengths and leap years.

Inputs and what they mean

Start date: — date value.
Operation: — choice value.
Years: — number value.
Months: — number value.
Weeks: — number value.
Days: — number value.

How to use it

Enter the dates, times, or schedule details.
Adjust the available options for your situation.
Review and copy the instant result.

Formula

Apply years and months first, clamping to the destination month end, then apply weeks and days.

Worked example

One month after January 31

Month-end clamping returns the last valid day in February.

Reading the result

The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.

Limitations and assumptions

Results depend entirely on the figures you enter and are rounded for display. They are for general information and education, not professional advice.