Date Calculator

Two questions, one tool

Date arithmetic comes in two shapes, and this calculator handles both.

How long between two dates? Counting days, weeks and business days between a start and an end — notice periods, project durations, time until a deadline.

What date is X from here? Adding or subtracting days, weeks, months or years from a known date — payment terms, warranty expiry, follow-up reminders.

Whether to count both endpoints

The convention matters and contracts often specify it. This calculator counts the nights between two dates: 1 March to 5 March is four days.

If you need both endpoints included — "the event runs from Monday to Friday, how many days is that?" — add one. Legal notice periods usually exclude the day of service and include the final day, which works out the same as adding one.

Business days

Switching to business days excludes Saturdays and Sundays. It does not exclude public holidays, because those vary by country, region and sometimes industry. If a deadline lands near a holiday period, subtract them by hand.

Note also that not every country's working week runs Monday to Friday — several in the Middle East use Sunday to Thursday.

Adding months is ambiguous

There's no universally correct answer to "one month after 31 January". The standard approach, used here, keeps the day of the month where it exists and clamps to the last valid day where it doesn't — so 31 January plus one month is 28 February, or 29 in a leap year.

That means the operation isn't reversible: subtracting a month from 28 February gives 28 January, not the 31st you started from. Where the exact day matters, work in days instead.