Two tools in one
- Days between dates: total days, the same span in years, months and days, full weeks and business days.
- Add or subtract: what date you land on when you add or subtract days, weeks, months or years.
Counting the days between two dates
The calculator counts every calendar day from the start date to the end date, without counting the start date itself. From January 1 to December 31, 2026 there are 364 days, of which 260 are weekdays.
Whether to include both ends depends on what you’re counting. For “how long until”, the standard is to exclude the start date. For a hotel stay you count nights, which works the same way. For something like “how many days did the event last”, where both the first and last day count, add one to the result.
Business days
Business days are Monday to Friday. The calculator doesn’t subtract public holidays because they depend on your state and your employer: the US has 11 federal holidays, and many states and companies observe a few more. If a deadline falls near one, check it on a calendar.
A common use: from September 10 to December 25, 2026 there are 106 days, 76 of them weekdays, or 15 full weeks.
Adding and subtracting time
Pick a starting date, an amount and a unit. 90 days after September 10, 2026 is December 9, 2026, the kind of date you need for return policies, notice periods or net-90 invoices.
Months need one rule: when the target month is shorter, you land on its last day. One month after January 31 is February 28, and six months after August 31, 2026 is February 28, 2027, not March 3. Adding years to February 29 works the same way: in a non-leap year you land on February 28.
Counting years since a date
If what you want is someone’s exact age, or how many days you’ve been alive, the age calculator does it directly from a date of birth.