How to Count the Days Between Two Dates (Including or Excluding the End Date)
"How many days until…?" sounds simple, yet two people can get answers that differ by one. The difference is whether you count the end date.
Exclusive vs inclusive counting
- Excluding the end date answers "how many days from A to B". From Monday to Friday is 4 days. Hotel nights, deadlines and interest calculations count this way.
- Including the end date answers "how many days does this period cover". Monday through Friday is 5 days. Trips, events and leave requests usually count this way.
In the days between dates calculator, tick Include the end date when you want the second kind.
Months are not all the same length
Saying "1 month" is ambiguous: January has 31 days, February 28 or 29. The calculator also shows the difference in calendar terms — years, months and days — counting real month lengths and leap years. January 31 to March 1 is 1 month and 1 day in a non-leap year.
Finding a date in the future or past
The second part of the tool adds or subtracts days. Use it for "90 days from today", a 30-day return window, or "45 days before the event". Use a negative number to go back.
When you need working days
If weekends and public holidays shouldn't count — delivery times, legal and payment deadlines — use the business days calculator instead. For someone's exact age, the age calculator handles birthdays and leap days.
Quick reference
- 1 non-leap year = 365 days = 52 weeks and 1 day.
- Leap years: divisible by 4, except centuries not divisible by 400 (2000 was a leap year, 2100 won't be).
- 100 days ≈ 3 months and 1 week.