Add or subtract days from a date

How to add or subtract days from a date

Count forward from the day after the start date, so the start itself is day zero: 30 days after 15 January 2026 is 14 February 2026, 16 days to 31 January and 14 more. To go back, count backward from the day before. Months and years work differently, keeping the day of the month.

For a large number of days, use day-of-year numbers. 5 October is day 278 of 2026, and 278 + 444 = 722. Taking off the 365 days of 2026 leaves day 357 of 2027, and since 1 December is day 335, that is Thursday 23 December 2027. Take off 366 for a leap year.

"Days from today" depends on where you are

Today means your local calendar date, so near midnight two people in different time zones get different answers. At 20:00 UTC on 31 December 2027, 444 days from today is 19 March 2029 in London but 20 March 2029 in India, where it is already 1 January 2028.

To give someone a result they can reproduce, write out the start date, such as 2026-10-05, instead of today, and say which unit you counted in.

Counting the start date as day 1

Some rules count the start date as day 1. A 7-day period that begins on 15 January 2026 and counts that day ends on 21 January, 6 days later, so add 6 rather than 7.

Months and years keep the day of the month

A month is not 30 days. From 31 January 2026, 30 days later is 2 March, but one month later is 28 February.

Adding months moves to the same day number in the target month. When that day doesn't exist, the result is the target month's last day, the rule used by Microsoft Excel's EDATE and the dateutil relativedelta library, so 31 January 2024 plus one month is 29 February.

A year is 12 months under the same rule, so it spans 365 or 366 days depending on whether a 29 February falls inside it, as the last two rows show.

Month steps can't always be undone. 31 March 2026 minus one month is 28 February, and 28 February plus one month is 28 March. Adding two months to 31 January 2024 gives 31 March, but adding one month twice gives 29 March, so work out each offset from the original date.

Adding business days

Business days are counted from the day after the start, skipping weekend days, and the start date never counts as one of them. Friday 16 January 2026 plus 1 business day is Monday 19 January, 3 calendar days later.

Adding 0 business days leaves the start date unchanged, even on a weekend: Saturday 17 January 2026 stays 17 January. The weekend can be Saturday and Sunday, Friday and Saturday, or Sunday only.

Public holidays are not skipped. For a deadline that must avoid them, use the working-day deadline calculator with your holiday list, and check whether a contract or court sets its own rule for the first day.

Limits and calendar rules

• Amounts are whole numbers from 0 to 1,000,000, or up to 100,000 business days. To go back in time, subtract rather than entering a negative number.
• Dates must exist. 2026-02-29 is rejected because 2026 is a common year; the leap year checker shows which years have a 29 February.
• Days are calendar dates, not 24-hour blocks, so a daylight-saving change never shifts the answer. For elapsed hours between dated times, use the hours calculator.
• Old dates are counted on the Gregorian calendar, even before a country adopted it.

To count the days between two known dates, use the date difference calculator, and for the weekday of a single date, the day of the week calculator.