Time Duration Calculator
Calculate the exact duration between any two dates or times in years, months, days, hours, and minutes. Handles overnight spans, leap years, and calendar month differences.
Enter your values above to see the results.
Tips & Notes
- ✓Always use 24-hour format for duration calculations to avoid AM/PM confusion. A 7:00 to 3:00 duration could be 8 hours or 20 hours depending on AM/PM.
- ✓For durations crossing midnight, add 24 to the end time before subtracting. Night shift 10:30 PM to 6:15 AM = 30:15 minus 22:30 = 7h 45m.
- ✓When a contract specifies calendar days, count every day including weekends and holidays. Business days exclude Saturdays, Sundays, and public holidays.
- ✓Leap years add one day — any duration spanning February 28 to 29 of a leap year is one day longer than the same span in a non-leap year.
- ✓90 calendar days is not 3 months — it falls on different dates depending on the starting month. Always count days directly rather than assuming 3 months equals 90 days.
Common Mistakes
- ✗Using 12-hour clock times without AM/PM — the duration from 9:00 to 4:00 is 7 hours AM to PM or 19 hours PM to next AM. Always specify or use 24-hour format.
- ✗Treating all months as 30 days — a 3-month duration from January 31 spans only 89 days through April 30 because February has 28 or 29 days.
- ✗Forgetting that leap years affect February — any duration involving February 28 to February 29 is one day different in a leap year versus a non-leap year.
- ✗Confusing calendar days with business days in deadline calculations — missing this distinction can result in being a week late on a 30-day deadline.
- ✗Not including the end date for inclusive counts — from Monday to Friday is 5 days inclusive, not 4 (the mathematical difference Friday minus Monday).
Time Duration Calculator Overview
Time duration calculation finds the exact elapsed time between a start point and an end point — in years, months, days, hours, minutes, and seconds simultaneously. It differs from simple subtraction because calendar months have unequal lengths and leap years add a day every four years, making naive arithmetic incorrect for durations spanning multiple months or years.
Duration between two clock times on the same day:
Duration = End Time − Start Time (in 24-hour format to avoid AM/PM ambiguity)
EX: Meeting starts 09:15, ends 11:42 → 11:42 − 09:15 → minutes: 42−15=27m → hours: 11−9=2h → Duration: 2h 27mDuration spanning midnight — overnight events:
EX: Night shift starts 22:30, ends 06:45 next morning → Add 24h to end: 30:45 − 22:30 → minutes: 45−30=15m → hours: 30−22=8h → Duration: 8h 15mDays in each month — essential for accurate multi-month duration:
| Month | Days (Normal) | Days (Leap Year) | Cumulative Days |
|---|---|---|---|
| January | 31 | 31 | 31 |
| February | 28 | 29 | 59 / 60 |
| March | 31 | 31 | 90 / 91 |
| April | 30 | 30 | 120 / 121 |
| May | 31 | 31 | 151 / 152 |
| June | 30 | 30 | 181 / 182 |
| July | 31 | 31 | 212 / 213 |
| August | 31 | 31 | 243 / 244 |
| September | 30 | 30 | 273 / 274 |
| October | 31 | 31 | 304 / 305 |
| November | 30 | 30 | 334 / 335 |
| December | 31 | 31 | 365 / 366 |
| Duration | Calendar Days | Business Days (approx) | Common Usage |
|---|---|---|---|
| 2 weeks | 14 | 10 | Sprint length, notice periods |
| 1 month | 28–31 | 20–23 | Monthly billing, payroll |
| 90 days | 90 | ~65 | Contracts, trial periods |
| 6 months | 181–184 | ~130 | Warranty periods, probation |
| 1 year | 365/366 | ~261 | Annual contracts, leases |
| 18 months | ~547 | ~392 | Product development cycles |
Frequently Asked Questions
For same-day times: subtract start from end in 24-hour format. For multi-day spans: count the full days between the dates, then handle the time component separately. Add the time difference (which may be negative if end time is earlier than start time, requiring borrowing a day) to the day count. For multi-month spans: count years and months first, then remaining days and time.
Calendar days count every day: weekdays, weekends, and holidays. Business days count only Monday through Friday, excluding public holidays. A 30-calendar-day period contains approximately 21–22 business days. A 30-business-day period spans approximately 42–43 calendar days. Legal deadlines, contract terms, and notice periods specify which type applies — this distinction matters significantly for compliance.
Add 24 hours to the end time, then subtract. Start 11:45 PM (23:45), End 7:30 AM (07:30 next day → 31:30): 31:30 − 23:45 → minutes: 30−45, borrow 1 hr: 90−45=45m → hours: 30−23=7h → Duration: 7h 45m. Alternatively, find how long until midnight (0:15) and add the time from midnight to the end time (7:30): 0:15 + 7:30 = 7h 45m.
Add 90 to the day number within the year (Julian day number) and convert back to a calendar date. Alternatively: count forward 3 months and adjust for the day — but 90 days is not exactly 3 months. From January 1: 90 days = April 1. From February 1: 90 days = May 2 (or May 1 in a leap year). From March 1: 90 days = May 30. Always count days directly rather than assuming 3 months equals 90 days.
Subtract the birth date from the target date component by component: subtract years, then months, then days, borrowing when necessary. If the birthday month/day has not yet passed in the current year, subtract 1 from the years and add 12 to the months. For the days, if the birth day is later than the current day, borrow the days in the previous month. This is identical to the method for any date duration.
Because there are multiple valid conventions for calculating months when the start and end days are different. From January 31 to March 31: some calculators say exactly 2 months, others say 1 month 28-31 days depending on how they handle the February component. From February 28 to March 28 is exactly 1 month. From February 28 to March 31 is either 1 month 3 days or 1 month 0 days (treating both as month-ends). Different calculators use different conventions — the day count (total days) is always unambiguous.