Add or subtract days from dates and find date differences
Built & maintained by Pappu Venkata Subbi Reddy, founder of Clacify · Updated August 2026
Date Calculator finds the duration between two dates and adds or subtracts days from a date. Enter two dates to get the exact gap in days, weeks, months, and years (plus a working-days count); or enter a start date and add/subtract a number of days to find the resulting date and its day of the week. It correctly handles leap years and varying month lengths. Useful for counting down to events, calculating deadlines and notice periods, working out durations for forms, or planning schedules. All calculation happens locally in your browser.
The difference between two dates is computed by converting both to a day count and subtracting, then expressing the result in years, months, and days by borrowing across months (using each month's real length) and leap years. Adding or subtracting time advances the date component-by-component, rolling over months and years correctly. The calendar borrowing and leap-year checks above are ordinary JavaScript date arithmetic, computed the moment you enter a date rather than fetched from anywhere.
| Month | Common year | Leap year |
|---|---|---|
| January | 31 | 31 |
| February | 28 | 29 |
| March | 31 | 31 |
| April | 30 | 30 |
| May | 31 | 31 |
| June | 30 | 30 |
| July | 31 | 31 |
| August | 31 | 31 |
| September | 30 | 30 |
| October | 31 | 31 |
| November | 30 | 30 |
| December | 31 | 31 |
Only February changes in a leap year — but that one extra day is exactly why naive "divide by 30" duration math gets a date range wrong.
A year is a leap year if it's divisible by 4 — except century years, which are leap years only if also divisible by 400. So 2024 and 2028 are leap years by the simple rule; 1900 was NOT a leap year (divisible by 100, not 400); but 2000 WAS a leap year (divisible by 400). This three-part rule keeps the calendar aligned with the Earth's actual orbit, and it's exactly the kind of edge case that breaks date math done by hand or with a naive formula.
Months range from 28 to 31 days, so a duration expressed only in days can be misleading — "62 days" could be exactly two months (if they're both 31-day months) or a bit more or less depending on which months are spanned. A proper date calculator counts whole calendar months first (borrowing a month's real length when the day-of-month doesn't divide evenly) and only expresses the remainder in days, which is why the years/months/days breakdown above is more useful than a raw day count for things like age or tenure.
"3 days from today" and "the gap between today and 3 days from now" can differ by one day depending on whether the start date itself is counted — this trips people up on notice periods, rental agreements, and deadline calculations. This tool counts the gap between two dates exclusively (the number of days you'd cross moving from one to the other); if your form or contract asks for an inclusive count (both the start and end date counted), add one day to the result.
Enter the start date and end date in Clacify's Date Calculator to instantly see the number of days, weeks, and months between them. For example, from 1 January 2025 to 26 May 2026 is 510 days.
Enter your start date in the Date Calculator and select '+ 30 days' to find the resulting date. Adding 30 days to 1 April 2025 gives 1 May 2025. Useful for calculating EMI due dates, return windows, license renewal dates, or notice period end dates.