How to Subtract Days from a Date

When you count backwards

Subtraction is the same question in reverse. You know the end of a period and want its start: a warranty that expires on a given date and lasted 90 days, a notice that must be sent 30 days before an event, a pregnancy that began a certain number of weeks ago.

It is also the way to find what the date was a fixed time ago. If today is 22 October 2026, what was the date 90 days ago? The answer is 24 July 2026, a Friday.

The counting rule going backwards

Move back one day at a time, starting from the date you have. One day before 1 March 2026 is 28 February 2026; 30 days before it is 30 January 2026. The day you start on is day 0, and the first day you step to is day 1, exactly as in forward counting.

Weekdays behave the same way. Subtracting a multiple of 7 days gives the same weekday, so 14 days before Thursday 22 October 2026 is Thursday 8 October 2026.

A worked example

Find the date 45 days before 10 March 2026. March gives 10 days back to 28 February: that is 10 days, leaving 35. February 2026 has 28 days, so going back 28 days leaves 7 and lands on 31 January. Seven more days gives 24 January 2026.

Check: 45 days is 6 weeks and 3 days, so the weekday moves back three days. 10 March 2026 is a Tuesday, three days earlier is a Saturday, and 24 January 2026 is a Saturday.

The check catches most slips. If the weekday does not match, recount the month lengths between the two dates.

Subtracting months and years

Subtracting a month moves the date to the same day number in the previous month. Three months before 22 October 2026 is 22 July 2026. If the previous month is shorter, the result is the last day of that month: one month before 31 March 2026 is 28 February 2026.

Subtracting a year works the same way, and the only special case is 29 February: one year before 29 February 2028 is 28 February 2027, because 2027 has no leap day.

Keep days and months separate. Thirty days before a date and one month before a date are different answers whenever the month does not have exactly 30 days.

Subtracting workdays

To step back by working days, move backwards one day at a time and count only Monday to Friday. Subtracting 1 workday from Monday 26 October 2026 gives Friday 23 October 2026, because the weekend is skipped.

This is how you find a start date for a task that needs five working days, or the last day on which something must be posted to arrive in time. Public holidays are not skipped automatically, so add one more day for each holiday in the range.

Leap years and the February trap

A leap day lengthens a backwards span as well. Going back 365 days from 1 March 2024 lands on 1 March 2023 plus one day: 2 March 2023, because 2024 has 366 days in the year before that date. This is why one year and 365 days are not the same thing across a leap day.

When a rule says one year, use years. When it says 365 days, use days. A calculator lets you do either, and shows both so that the difference is visible.

Everyday examples

Subtraction is common in planning. A warranty that expires on 22 October 2026 and runs for 90 days started on 24 July 2026. A notice that must reach the other side 14 days before an event on 22 October 2026 has to be sent by 8 October 2026. A course that began 60 days before 22 October 2026 started on 23 August 2026.

For longer spans, 180 days before 22 October 2026 is 25 April 2026, a Saturday, and 365 days before it is 22 October 2025, because no leap day lies in between.

Check the answer with the weekday

Divide the number of days by 7 and look at the remainder. Going back, a remainder of 0 keeps the weekday, a remainder of 1 moves it one day back, and so on. Ninety days leaves a remainder of 6, so 90 days before a Thursday is the Friday before the previous six days: 24 July 2026 is a Friday, which matches.

If the result lands on a weekend and you needed a working day, step forward or backward to the nearest working day, and write down which direction you chose so that it is clear later.

Using a calculator

Open the Add or subtract tab, enter the date you start from, choose Subtract and type the amount. You can mix years, months, weeks, days and workdays. The result shows the earlier date together with its weekday, and you can copy it with one tap.

For a quick check of your own arithmetic, switch to the days-between tab and enter the answer and the original date. The difference should be the number you subtracted.