Days between two dates

How to count the days between two dates

Every date on the calendar has a position in one long unbroken count of days. Take the position of the later date, subtract the position of the earlier one, and the result is the number of days between them. Months, leap years and year boundaries stop mattering, because the count already includes them. That is how this calculator works, and it is how spreadsheets and databases work too: they store a date as a day number and subtract.

If you do it by hand, count the days left in the first month, add the full months in between, then add the day number of the final date. From March 15 to June 15: 16 days left in March, 30 in April, 31 in May, 15 in June, which makes 92. Three months starting on December 15 are only 90 days, and from January 15 to April 15 is 90, or 91 in a leap year.

Inclusive or exclusive: the one-day question

Most disagreements about a day count come down to whether the first day counts. Think of a fence: ten metres of fence with a post every metre needs eleven posts, not ten. Dates behave the same way. Between Monday and Friday there are four intervals but five dates.

Use the default, which leaves out the start date, when you are measuring elapsed time: how long ago something happened, how old something is, how far off an event is. Tick “Count both dates” when each date is a unit you use up: days of annual leave, days of a course, or days of a conference. A trip from July 10 through July 20 occupies 11 calendar dates but only 10 nights.

Contracts and legal rules usually say which they mean, and you should follow the wording rather than a calculator’s default. The United States federal court rules are a clear example: Rule 6 of the Federal Rules of Civil Procedure excludes the day of the triggering event, counts every day after it including weekends and holidays, and then carries a last day that lands on a weekend or legal holiday over to the next working day. Other courts and countries use other rules, so treat this as an illustration and not legal advice. Business days calculator covers working-day periods.

Weeks, months and years are not all the same kind of unit

Days and weeks are fixed lengths, so converting between them is plain division. Months and years are not. A month has 28 to 31 days and a year has 365 or 366, so “how many months” has to be counted along the calendar instead of divided. This tool uses the rule most software uses: step forward whole months from the start date, and if the target month is too short, stop at its last day. Then count the days that remain.

That rule has a consequence that surprises people. From January 31 to March 1, 2027 is 1 month and 1 day, because one month after January 31 is February 28, and March 1 is one day later. In 2028, a leap year, the same dates give 1 month and 1 day as well, but the span holds one more day: 30 instead of 29. Two spans with the same month count can differ by up to three days, which is why invoices, rent and interest calculations state their own day-count convention.

Dividing days by 30 or by 30.44 gives a figure that sounds precise and is only an average. Use it for a rough sense of size, not for a date you need to meet.

Worked examples

The first row is a useful check on any tool: January 1 to December 31 of a common year is 364 days, not 365, unless you count both dates. The whole of 2027, counted inclusively, has 261 weekdays before any public holidays are removed.

Leap years in a day count

A leap day adds one to any span that contains February 29. Under the Gregorian rule, a year divisible by 4 is a leap year, except century years not divisible by 400. So 2000 was a leap year, 2100 will not be, and there are 97 leap days in every 400 years. The result lists the leap day when your span contains one. Leap years go into more detail.

A span that merely touches a leap year may not include the leap day. January 1 to February 28, 2028 has no leap day in it, and March 1 to December 31, 2028 has none either. It matters only whether February 29 falls after the start date and on or before the end date.

Dates long ago

For old dates, a day count has a catch: the calendar itself changed. In the Catholic changeover of 1582, Thursday October 4 was followed directly by Friday October 15, dropping ten dates. Britain and its colonies followed in 1752, when September 2 was followed by September 14. Other countries switched later still, some in the twentieth century. This tool uses the Gregorian calendar throughout, extended backwards, as most software does (ISO 8601 allows this by agreement between the parties). A date copied from a record written in the old calendar should be converted first, or the count will be off by ten days or more.

Doing it in a spreadsheet or in code

• Excel and Google Sheets: =B1-A1 gives the days between two date cells, leaving out the start date. Add 1 to count both ends. Format the result as a number or you may see a date.
• Working days: =NETWORKDAYS(A1,B1,holidays) counts both the start and the end date if they are working days. Our business-day figure leaves out the start date unless you tick “Count both dates”, so compare with that box ticked.
• DATEDIF: Microsoft keeps it to support old Lotus 1-2-3 workbooks and warns that it can give wrong results in some cases. Its “MD” unit in particular can return a negative number, zero or an inaccurate figure.
• Excel’s 1900 bug: Excel treats 1900 as a leap year, a choice kept for compatibility with Lotus 1-2-3. Counts that begin before March 1, 1900 can be one day out.
• Code: subtract dates, not timestamps. Dividing the milliseconds between two local midnights by 86,400,000 fails around a clock change, because that day has 23 or 25 hours in the zone. Convert each date to a day number first, or use the date-only type your language provides.

Calendar days, business days and what the result does not know

The figure for weekdays removes Saturdays and Sundays, or whichever weekend you choose, and then the public holidays of the set you pick. National holiday sets come from official lists for 2026 to 2028. Outside those years the tool skips weekends only and says so. Regional holidays, bank closures and company shutdowns are not included. If a deadline depends on them, check the exact days with whoever set it.

For a date a set distance from another, use the date calculator. For a live count to an event, use days until a date. To see what any single date looks like, weekday and week number included, use date facts.