How to count the days between two dates
By the FreeAllTool team · Updated October 28, 2026
How many days until an exam, how long a rental agreement lasts, how many days late a payment is: counting days between dates comes up often. It looks simple, but there is one detail that causes most mistakes.
Inclusive or exclusive?
From 1 March to 5 March, is that 4 days or 5? Both answers can be correct, depending on what you are counting.
- Exclusive counting measures the gap between the dates. From 1 March to 5 March is 4 days. This is how most date calculators, interest calculations and age calculations work.
- Inclusive counting counts both the first and last day. A hotel stay or event running from 1 March to 5 March covers 5 calendar days. Add 1 to the exclusive count.
When a rule or contract matters, check which method it uses.
Counting by hand
For dates in the same month, subtract the day numbers. For dates in different months, count the days remaining in the first month, add the full months in between, and add the days in the last month. Remember that months have 28 to 31 days, and February has 29 days in a leap year.
Example: from 20 January to 15 March in a non-leap year. Days left in January after the 20th: 11. February: 28. March up to the 15th: 15. Total: 54 days.
Weeks and months
To convert days to weeks, divide by 7. Converting to months is trickier because months differ in length. That is why our age calculator works in calendar months: from 31 January to 28 February counts as less than one full month, even though it is 28 days.
Everyday uses
- Counting down to exams, weddings or trips.
- Checking notice periods and return windows.
- Working out how long a medicine course or subscription lasts.
- Tracking pregnancy or a baby’s age in days and weeks.
Spreadsheet programs can also do this: subtracting one date cell from another gives the number of days between them.