How the difference is calculated
Each date is turned into a day number on the Gregorian calendar, so the total is simply end minus start. That count automatically includes every 29 February in between and never shifts with time zones or daylight-saving changes.
For the years-months-days breakdown, whole calendar months are counted from the start date first, then the leftover days. If the start day does not exist in a later month (such as the 31st), the last day of that month is used.
Formula: total days = day number(end) − day number(start)
Worked example: 15 January 2024 to 1 March 2025
- Whole months: 15 Jan 2024 → 15 Feb 2025 is 13 months (1 year 1 month).
- Leftover days: 15 Feb 2025 → 1 Mar 2025 is 14 days (February 2025 has 28 days).
- Total days: 2024 is a leap year, so 15 Jan 2024 → 15 Jan 2025 is 366 days, plus 45 more = 411 days.
Practical uses
- Counting down to an event, trip or deadline.
- Checking how long a contract, lease or warranty has run.
- Finding a project's length in weeks for planning.
- Working out how many days a loan or deposit was held, before applying an interest rule.
Limitations
- The end date is excluded. Add one day to count both ends.
- Historical dates before the Gregorian reform (1582, or later in some countries) are calculated on the modern calendar.
To count only working days, use the Business Days Calculator. To find a date a set time away, use Add or Subtract Dates.
Frequently asked questions
Does the count include the end date?
No. The result is the number of days you would add to the start date to reach the end date, so 1 March to 2 March is 1 day. Add one if you want to count both dates.
How are leap years handled?
Every date is placed on the Gregorian calendar, which includes 29 February in years divisible by 4, except century years not divisible by 400. 2000 was a leap year; 1900 and 2100 are not.
Why can “1 month” mean 28 to 31 days?
Months are counted on the calendar. From 31 January, one month later is the last day of February, because 31 February does not exist.
How many days are there from 1 January 2025 to 25 December 2025?
358 days, which is 51 weeks and 1 day (11 months and 24 days on the calendar).