A date difference calculator is a free online tool that measures the time between two dates or moves a date forward and backward by a number of days. Switch between the Difference tab for years, months, days and totals, and the Add or Subtract tab for deadline and scheduling math, with no signup.
How many days between two dates?
Add or subtract days from a date
How do you calculate the number of days between two dates?
Subtract the earlier date from the later date and count the 24-hour periods between them. January 1 to January 31 is 30 days exclusive, or 31 days inclusive. Leap days inside the range are counted automatically by real calendar math.
The calculator above does this instantly and also breaks the span into years, months and days, which is the format contracts and HR policies usually want. Totals in weeks, hours and minutes help with billing and project planning.
Should I count the start and end date when measuring a period?
It depends on the convention: hotel nights and rentals use exclusive counting (nights stayed), while project day-counts and some payroll rules use inclusive counting (both endpoints). When in doubt, state which one you used so everyone interprets the number identically.
The inclusive checkbox above adds one day to include both endpoints, so you can match whichever convention your contract or policy requires without mental arithmetic.
How do I add 90 days to a date?
Open the Add / Subtract tab, enter your start date and 90, choose Add, and the tool returns the exact calendar date 90 days later with its weekday. For example, 90 days after January 1 lands on April 1 in a non-leap year.
This is the standard way to compute payment terms (net-30, net-90), visa stays, warranty expirations and notice periods without counting on your fingers.
Why do manual day counts often go wrong?
People forget leap days, miscount month lengths, and mix up inclusive versus exclusive counting. A single off-by-one error can shift a deadline, a medication schedule or a legal filing date, which is why a calculator beats mental arithmetic. It also makes the inclusive-or-exclusive rule explicit every time.
Using a calculator removes all three failure modes: month lengths and leap years come from the real calendar, and the inclusive toggle makes the counting rule explicit.
FAQs
Is this date difference calculator free?
Yes. Calculate date differences and add or subtract days as often as you like with no account and no limits.
What is the difference between inclusive and exclusive day counts?
Exclusive counts the days strictly between two dates (Jan 1 to Jan 2 is 1 day). Inclusive counts both endpoints as well (Jan 1 to Jan 2 is 2 days). Toggle the checkbox to match your use case.
Does it handle leap years?
Yes. All math uses real calendar dates, so February 29 and leap-year boundaries are counted correctly.
Can I add business days instead of calendar days?
This tool counts calendar days. A quick workaround: add the calendar days, then shift past any weekends that fall inside the range.
Is my data sent anywhere?
No. The dates you enter are processed entirely in your browser and never leave your device.