DATE CALCULATION GUIDE
To calculate the number of days between two dates, subtract the earlier date from the later date. There are several methods to do this accurately, depending on whether you are calculating by hand, using a spreadsheet, or using a formula.
The simplest approach: start from the earlier date and count forward to the later date, one day at a time. This is practical for short ranges (a few weeks) but impractical for longer ones.
Example: How many days from April 1 to April 15?
April 1 → April 15 = 14 days.
Each day of the year has a number from 1 (January 1) to 365 (December 31). To find days between two dates in the same year, subtract the day numbers.
Example: How many days from March 10 to November 20, 2025?
| Month | Day of year (first day) | Days in month |
|---|---|---|
| January | 1 | 31 |
| February | 32 | 28 (or 29 in a leap year) |
| March | 60 (61 in leap year) | 31 |
| April | 91 (92) | 30 |
| May | 121 (122) | 31 |
| June | 152 (153) | 30 |
| July | 182 (183) | 31 |
| August | 213 (214) | 31 |
| September | 244 (245) | 30 |
| October | 274 (275) | 31 |
| November | 305 (306) | 30 |
| December | 335 (336) | 31 |
When dates span multiple years, add up the remaining days in the first year, the full days in complete middle years, and the days elapsed in the final year.
Example: Days from June 15, 2020 to March 10, 2024:
A leap year has 366 days instead of 365. When your date range includes February 29 of a leap year, add 1 extra day. Leap years occur every 4 years: 2020, 2024, 2028, 2032…
If you are calculating by hand across multiple years, check whether each year in the range is a leap year and use 366 instead of 365 for those years.
364 days separate January 1 and December 31 (not counting the first day). The full year from January 1 to January 1 of the next year is 365 days (or 366 in a leap year).
In Excel, subtract the two date cells directly: =B1-A1. Format the result cell as a number (not a date). Excel stores dates as numbers, so subtraction gives the exact number of days.
It depends on the convention. Most calculators count the gap between dates (not including either endpoint), so January 1 to January 5 = 4 days. If you need to include both days (e.g., for a rental period), add 1 to the result.
If the date range includes February 29 of a leap year, add 1 extra day compared to a non-leap-year calculation. For example, January 1, 2024 to January 1, 2025 = 366 days (2024 is a leap year).
Use an online date calculator (like the one on this site). Enter the two dates and the calculator instantly returns the number of days, weeks, months, and years between them.