Time Duration Calculator
Find the exact duration between two times — in h:m:s, total minutes, and decimal hours at once. Handles overnight shifts that cross midnight, multi-day spans with real dates, and adding or subtracting several durations together.
8h 30m (8.50h)
Total minutes: 510 · Total seconds: 30600
If the end time is earlier than the start time in "between two times" mode, we assume it crosses midnight. Use "dates + times" mode for exact multi-day spans. How we calculate →
How duration between two times is calculated
Convert both times to a single unit — seconds since midnight works well — and subtract the start from the end. 9:00 AM to 5:30 PM becomes 17:30 minus 9:00, or 8 hours 30 minutes. The calculator does this automatically and shows the answer three ways at once: hours/minutes/seconds, total minutes, and decimal hours (8.5, in this example) — the format most payroll and billing systems actually want.
Handling the midnight crossing
When you only give two times of day (no dates) and the end time is earlier than the start time — say, 10:00 PM to 6:00 AM — the calculator assumes the span crosses midnight and adds 24 hours before subtracting, giving 8 hours rather than a negative number. This is the standard convention for overnight shifts and is exactly how the calculator's engine (shared with our Hours Calculator for weekly time cards) handles night shifts.
Multi-day spans with real dates
For anything longer than a single overnight — a project spanning several days, or an event running Friday evening to Sunday morning — use the dates + times mode. It computes the exact span between two real calendar date-times, so a duration of 1 day 8 hours (32 hours total) comes out correctly instead of being capped at 24 hours.
Adding and subtracting durations
Timesheets and project estimates often need several durations combined — 2h30 of meetings plus 1h45 of focused work minus a 20-minute break, for instance. The add/subtract mode lets you enter any number of h:m:s rows with a +/− sign each, and sums them into one net duration, correctly carrying over minutes and seconds into hours (2h30 + 1h45 − 0h20 = 3h55).
Decimal hours vs. h:m:s — why both matter
Timesheets for payroll typically want decimal hours (8.5h, not 8h30m) because pay rates multiply cleanly against a decimal number. Everyday scheduling usually reads more naturally in h:m:s. The calculator always shows both, so you don't have to convert 30 minutes to 0.5 by hand every time you fill out a timesheet.
Frequently asked questions
How do I calculate the number of hours between two times?
Convert both to 24-hour format and subtract the start from the end. 9:00 AM to 5:30 PM is 17:30 − 09:00 = 8 hours 30 minutes, or 8.5 decimal hours.
What happens if the end time is before the start time?
The calculator assumes the span crosses midnight and adds 24 hours before subtracting — so 10:00 PM to 6:00 AM correctly comes out to 8 hours instead of a negative number.
How do I convert hours and minutes to decimal hours?
Divide the minutes by 60 and add to the whole hours: 8 hours 30 minutes is 8 + 30÷60 = 8.5 decimal hours. This is the format most payroll systems expect.
Can I calculate duration across multiple days?
Yes — use the dates + times mode with a start date/time and end date/time; it computes the exact multi-day span (for example, 1 day 8 hours = 32 hours total) rather than assuming a single 24-hour cycle.
How do I add or subtract multiple time durations?
Enter each duration as hours, minutes, seconds with a + or − sign, and the calculator sums them into one net duration, correctly carrying minutes and seconds over into hours.
How many minutes are in 8.5 decimal hours?
510 minutes — multiply the decimal hours by 60 (8.5 × 60 = 510).
Researched & verified by the Calcuris Data & Research Team. How we build and check our tools →