Calculating the number of days between two dates is straightforward once you understand the formula. Use HowUntil's date difference calculator to do this instantly.
The Formula
Days Between = Target Date − Start Date
For example: December 25 − September 19 = 97 days (counting calendar days, not including September 19).
Manual Calculation
To calculate manually:
- Count days remaining in the start month
- Add days for each complete month in between
- Add days in the final month up to the target date
- Account for any leap years if February is crossed
Leap Year Handling
If your date range includes February 29 in a leap year, that adds one extra day to your count. HowUntil handles this automatically.
Business Days vs. Calendar Days
Calendar days count every day including weekends. Business days (also called working days) exclude Saturdays and Sundays. Use the business days calculator for work-related deadlines.
Put It Into Practice
Use our free, instant calculator tools to run these calculations on your exact dates without any manual math.