Date Difference Calculator
Count the days, weeks and months between two dates — or add a period to a date to find a deadline.
Runs entirely in your browser. Nothing you type here is uploaded, stored or logged.
Inclusive or exclusive — pick the right one
This is the single decision that changes the answer by a day, and it trips up invoices, leave requests and contract deadlines constantly.
Exclusive (the default) counts the nights between two dates. Monday to Friday is four. Use it for hotel stays, car hire, interest periods and anything billed per night.
Inclusive counts both endpoints as full days. Monday to Friday is five. Use it for annual leave, event durations, jury service, quarantine periods and most contractual notice.
Business days and why holidays aren't included
The business-day count removes every Saturday and Sunday in the range. It deliberately does not remove public holidays: those vary by country, by state, and sometimes by industry, so a built-in list would be wrong for most visitors most of the time. If you're counting toward a legal or tax deadline, subtract your local holidays by hand and check the rule — some deadlines roll forward to the next working day, others don't.
Adding months is not the same as adding 30 days
When you add a month to 31 January, there is no 31 February. The convention used here is to clamp to the last valid day of the target month, so you get 28 February (or 29 in a leap year). Adding one month to 31 March gives 30 April. This matches how banks and most contracts handle monthly anniversaries, but it means adding one month twice is not always the same as adding two months at once.
Common uses
- Notice periods — add 30, 60 or 90 days to a resignation date.
- Payment terms — net-30 from an invoice date.
- Returns and warranties — is the 14-day window still open?
- Project planning — working days between kickoff and delivery.
- Milestones — how long since a start date, in days rather than a vague “a few months”.
Frequently asked questions
Does the count include both the start and end date?
By default, no — it counts the nights between them, which is how hire cars, hotels and interest periods work. Tick “include both dates” to count them as full days instead, which is how you count leave, event days or a notice period.
How are business days worked out?
Every Saturday and Sunday is excluded. Public holidays are not, because they differ by country and even by region, so check your local calendar before relying on the figure for a legal deadline.
Can I add or subtract days from a date?
Yes — switch to the “Add / subtract” tab. Enter a starting date and a number of days, weeks, months or years, and choose whether to move forwards or backwards. Useful for due dates, warranty expiry and notice periods.
Why is the number of months not a whole number of weeks?
Because calendar months vary between 28 and 31 days. The months figure counts completed calendar months from the start date; the weeks figure is total days divided by seven. They describe the same span in two different units and will rarely line up neatly.