How the duration is calculated
Each valid Gregorian date is converted to an ordinal day. The time is converted to seconds after midnight. The calculator then subtracts the Start civil timestamp from the End civil timestamp using integer arithmetic.
Two dated endpoints
Time Duration Calculator
Calculate the elapsed duration between two dates and times. See days, hours, minutes, seconds, plus exact total days, hours, minutes, and seconds.
Local-first calculation.
Your entered dates and times stay in this browser page. This calculator uses timezone-free Gregorian civil time: every duration day is exactly 24 hours.
Start and End
Use calendar dates plus 24-hour times. Seconds are optional.
StartEnd
Gregorian dates and leap years
Years divisible by 4 are leap years except century years, unless the year is also divisible by 400. That makes 2000 a leap year while 1900 and 2100 are not.
Every duration day is 24 hours
This app uses timezone-free civil time. One duration day is exactly 86,400 seconds. It does not apply daylight-saving transitions or location-based clock rules.
Days, hours, minutes, and seconds
The primary result decomposes exact elapsed seconds into fixed 24-hour days, then hours, minutes, and seconds. Months and years are not used as elapsed units because their lengths vary.
Exact totals
Total seconds is an exact integer. Total minutes, hours, and days are deterministic ratios rounded half-up to at most six decimal places with unnecessary trailing zeros removed.
Equal and reversed endpoints
Identical Start and End values are a valid zero duration. If End occurs before Start, the app shows an error instead of silently swapping or taking an absolute value.
Example: several days
From 2026-10-17 08:30:00 to 2026-10-20 15:54:15 the duration is 3d 7h 24m 15s, or 285,855 total seconds.
Example: crossing leap day
From 2024-02-28 23:30:00 to 2024-03-01 00:15:30 the duration is 1d 0h 45m 30s. February 29 is included because 2024 is a leap year.
Choose the right time app
Time Calculator adds or subtracts duration quantities. Hours Calculator measures one simple Start-to-End clock span without dates. Time Card Calculator totals weekly work punches and lunches.
What this app does not decide
It does not perform timezone conversion, DST-aware actual elapsed time, payroll, business-day counting, age calculation, inclusive date counting, or calendar-month/year duration estimates.
Learn the method
Read How to Calculate Duration Between Two Dates and Times for the ordinal-day method, leap-year rules, exact totals, and boundary cases.
Privacy and page memory
Calculation work remains in page memory. Refreshing or closing the tab may discard it. Copy result acts only when you choose it, and Share App uses the canonical app URL rather than your entered values.