Date Duration Calculator
Count the days between two dates, broken down into years, months, weeks, business days and hours, or add and subtract days, weeks, months or years from a date.
Inclusive counts both dates: Monday to Friday = 5 days instead of 4.
How this date duration calculator counts days
The date duration calculator counts the number of midnights between two calendar dates. From Monday to Friday of the same week that is 4 days: the start day is not counted, the end day is. If you need both ends counted (how many days a hotel booking covers, how many days you were on a project), switch to inclusive counting and you get 5. All of the math runs on plain calendar dates, not clock times, so daylight-saving changes and time zones never add or lose an hour.
The years/months/days breakdown steps forward one calendar month at a time from the start date for as long as it stays on or before the end date, then counts the leftover days. When a month does not have the start day (January 31 plus one month), it uses the last day of that month. That is the same rule most date libraries and the add/subtract mode use, so the two modes agree with each other.
Worked example
How long from March 15, 2026 to October 20, 2026? Counting midnights gives 219 days. Stepping by months: March 15 → April 15 → … → October 15 is 7 months, and October 15 → October 20 is 5 more days, so 7 months and 5 days. In weeks, 219 ÷ 7 = 31 weeks and 2 days. The range contains 62 weekend days, so there are 157 business days. Multiply by 24 for 5,256 hours.
Business days and holidays
Business days here means Monday through Friday. Public holidays are not removed because they differ by country, state and employer; a deadline of "10 business days" at a US federal agency skips Thanksgiving, while a private company might not. If a holiday falls inside your range, subtract it from the business-day count yourself. Likewise, the calculator does not know about your company's fiscal calendar or a four-day week.
Adding and subtracting dates
The second mode answers questions like "what date is 90 days from today" or "what was the date 6 months ago". Days and weeks are exact. Months and years keep the same day of the month where possible: August 31 plus one month is September 30, and February 29, 2024 plus one year is February 28, 2025. Contracts and leases sometimes specify a different convention (for example, the first of the following month), so read the document before relying on the calendar rule.
Common mistakes
- Off-by-one errors. "30 days from the 1st" is the 31st, not the 30th. Decide whether your situation counts the start day before you pick inclusive or exclusive.
- Treating a month as 30 days. Six months from January 15 is July 15, which is 181 days, not 180. Use the months unit when a document says months.
- Trusting a spreadsheet across a DST change. Subtracting two timestamps instead of two dates can produce 29.96 days instead of 30. This tool only uses dates.
Frequently asked questions
›How are the days between two dates counted?
By counting the midnights between them, so the start date is not counted and the end date is. Monday to Friday is 4 days. Switch to inclusive counting to count both dates (5 days).
›What are business days?
Monday through Friday. The calculator excludes Saturdays and Sundays but not public holidays, because those vary by country, state and employer; subtract any holidays in your range yourself.
›What happens when I add a month to January 31?
You get February 28 (or February 29 in a leap year). When the target month has no matching day, the calculator uses the last day of that month, the same rule most calendar software uses.
›Does daylight saving time affect the result?
No. All math is done on calendar dates, not clock times, so a range that crosses a daylight-saving change is still counted in whole days.
›How many days are in a year?
365 in a common year and 366 in a leap year. Leap years are divisible by 4, except century years, which must be divisible by 400: 2024 and 2000 are leap years, 2100 is not.