Clock Math — Time Duration Calculator
Time Calculator
Free online time & date calculators
Time duration calculator — hours between two times
Enter any two times — or two full dates — and get the exact elapsed time between them: 9:00 to 17:30 is 8 hours 30 minutes, shown as h:m:s, as total minutes (510), and as decimal hours (8.5) for timesheets and payroll. Times that cross midnight are handled automatically, so a 10:00 PM to 6:00 AM night shift correctly reads 8 hours.
Common uses: work shifts and adding up a week of work hours, workout and study session lengths, travel legs, and how long you slept. For minutes-to-decimal conversions, see the decimal hours table.
Frequently asked questions
How do I calculate the hours between two times?
Enter a start and end time and press Calculate Duration. 9:00 AM to 5:30 PM is 8 hours 30 minutes — shown as h:m:s, total minutes, and 8.5 decimal hours.
Does it work across midnight?
Yes. When the end time is earlier than the start time, the calculator treats it as the next day: 10:00 PM to 6:00 AM is 8 hours, not negative time.
Can it calculate the duration between two dates?
Yes — both ends take a date as well as a time, and the result breaks the duration down calendar-accurately into years, months, days, hours, minutes, and seconds.
What are decimal hours?
Decimal hours express minutes as a fraction of an hour (minutes ÷ 60), which is what payroll math needs: 8 hours 30 minutes is 8.5 hours. The result shows both formats.
Can I add up several time periods?
Yes. Every calculation is kept in the Recent Calculations list — select any of them and press Sum Selected to total multiple durations, for example separate work sessions in a day.
All ClockMath tools
- Work hours & timesheet calculator — total shifts with breaks, decimal hours, and gross pay
- Timezone converter — any two places, with automatic daylight-saving handling
- Stock market hours — live open/closed status for major exchanges in your timezone
- Decimal hours converter — minutes to decimal (and back) with the full payroll chart
- Countdown timer — count down to any date and share it
- Guides — practical articles on work hours, payroll time math, and timezones