The formula
How it works
Count the number of days between two dates, or add and subtract days from a date to land on a new one. Handy for deadlines, notice periods, due dates and any countdown.
FAQ
Does the count include both end dates?
The “days between” figure is the gap from one date to the other, so it does not double-count the start day. If you need inclusive counting (both days counted), add one to the result.
How do I subtract days?
Switch to “Add / subtract” and enter a negative number of days. For example, −30 finds the date 30 days before your start date.
Does it account for leap years automatically?
Yes. Every date is converted to a real calendar date internally, so February in a leap year correctly has 29 days without any extra input from you.
What does “Approx. months” mean in the result?
It divides the total days by 30.44, the average length of a month, since calendar months vary from 28 to 31 days. Treat it as a rough guide rather than an exact count.
Does it matter which date I enter first in “Days between”?
No. Enter the earlier or later date in either box — the calculator shows the gap between them regardless of order, though the sign of the result follows to-date minus from-date.
How do I know what day of the week the result date falls on?
In “Add / subtract” mode, the result includes the weekday name alongside the new date, so you can see immediately whether you land on a Monday, a Friday, and so on.
Does the time of day affect the calculation?
No, the calculator works with whole calendar dates only, so it ignores any time component and always counts in full days.
About the date calculator
This calculator answers the two most common date questions: how many days lie between two dates, and what date you land on if you add or subtract a number of days. Counting days by hand across month boundaries and leap years is fiddly and easy to get wrong, so working directly with calendar dates removes the guesswork. It is the tool for deadlines, waiting periods, anniversaries and countdowns.
How to use it
Choose what you want to do. For “Days between”, pick a from-date and a to-date, and the calculator shows the number of days, weeks and months between them. For “Add / subtract”, pick a start date and enter the number of days to move — positive to go forward, negative to go back — and it returns the resulting date and the day of the week it falls on. Everything recalculates as you change the inputs.
The formula
The days between two dates is their difference, , found by converting each date to a running day count and subtracting. Adding days does the reverse: it turns the start date into a day count, adds the number of days, and converts back to a calendar date. Because the calculation is done in whole days on real dates, leap years and month lengths are handled automatically.
Where it is used
People use it to count down to holidays, weddings and launches, to work out contract notice periods and payment terms, and to find deadlines a set number of days away. Project managers use it for schedules, and anyone dealing with legal or official time limits — a 30-day notice, a 90-day window — uses it to land on the exact date. It is the everyday companion to the age and duration calculators.