Calendar Calculator: Days Between Dates and Date Math
Count the days between two dates, or add and subtract days, weeks, months and years from a date and see which day of the week it lands on.
To count the days between two dates, subtract the earlier from the later using real month lengths, so leap years add a day in February. From January 1 to December 25, 2026 is 358 days, or 359 if you count both the first and the last day. To move a date, add months and years first, then days: 90 days after Tuesday, September 29, 2026 is Monday, December 28, 2026.
This calculator counts calendar days on the Gregorian calendar without time zones, holidays or business-day rules. For official or contractual deadlines, check how the governing rules count days before relying on the result.
Days between two dates
Days between
358 days
- Counting both the start and end dates
- 359 days
- In weeks
- 51 weeks, 1 day
- In years, months and days
- 0 years, 11 months, 24 days
- Start date falls on
- Thursday
- End date falls on
- Friday
Add or subtract time from a date
Resulting date
2026-12-28
- Day of the week
- Monday
- Starting date falls on
- Tuesday
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About the Calendar Calculator
Counting days by hand goes wrong in two places: months have different lengths, and it is easy to lose track of whether the first or last day is included. This calculator counts on the calendar itself. The day count is the number of midnights between the two dates, which is what "days until" usually means: from Monday to Friday is 4 days. Many deadlines and rentals count both ends, so it also shows that figure, which is always one more. The years, months and days breakdown steps through whole months first, so January 31, 2000 to September 29, 2026 is 26 years, 7 months and 29 days. Adding time applies years and months before days. When a month has no matching day, the date moves to the last day of that month: one month after January 31 is February 28, or February 29 in a leap year, and a year after February 29, 2024 is February 28, 2025. The breakdown between two dates follows the same rule, so January 31 to February 28 counts as one whole month. Days and weeks then count forward or back exactly. Every date also shows its weekday. The math uses the Gregorian calendar with no time zones, so it gives the same answer wherever you are.
Frequently asked questions
Does the count include the start and end dates?+
The main figure counts the days from the start date up to the end date, not including the end, the way "how many days until" is usually meant. January 1 to December 25, 2026 gives 358. Counting both the first and last days, as some contracts and events do, gives 359, which the calculator shows underneath.
What happens when I add a month to January 31?+
February has no 31st, so the result moves back to the last day of February: February 28, 2026, or February 29 in a leap year such as 2024. The same rule applies to subtracting: one month before March 31 is the last day of February.
How are leap years handled?+
A year is a leap year when it divides by 4, except century years, which must divide by 400. So 2024 and 2000 had a February 29, and 1900 and 2100 do not. The calculator reads the real length of every month, so a range that crosses February 29 counts it.
Does this skip weekends or holidays?+
No, it counts every calendar day. To count only Monday through Friday, use the business day calculator, which leaves out weekends. Neither tool knows public holidays, since those change by country and year.
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Free to use on your own site. Paste this snippet where you want the calendar calculator to appear — it resizes itself automatically.
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