numcal. / DATE TOOLS / ADD DAYS

Add or subtract time from a date.

Days, weeks, months, years — or business days that skip the weekends. Deadlines, notice periods, “90 days from signature”.

 
ISO date
Calendar days moved
Week number

Field notes

What happens on January 31 + 1 month?

It clamps to the last day of the shorter month: February 28 (or 29 in a leap year). Same rule for May 31 + 1 month → June 30. That’s the convention contracts and spreadsheets use.

How do business days work?

Each step skips Saturdays and Sundays: Friday + 1 business day is Monday. Public holidays are not skipped — they vary by country, so check your local calendar for the exact deadline.

Where does this run?

Entirely in your browser. Dates you type are never sent anywhere — there is no server doing the math, no analytics watching you do it.