Add, subtract, and calculate duration between times.
Calculate time between two points.
A time calculator works out the gap between two clock times, or adds and subtracts hours and minutes from a starting point. It handles the awkward part of time math automatically: the fact that time runs in base 60, not base 10, and that a shift can cross midnight into the next day. It is the tool of choice for filling in timesheets, planning schedules, and pricing work by the hour.
Time is one of the few things we still count in base 60, a habit inherited from ancient Babylonian astronomers. That single fact is why time arithmetic trips people up. In everyday decimal math, carrying happens at 10. With time, it happens at 60 for minutes and again at 24 for hours.
Converting everything to minutes first, doing plain subtraction, then converting back is the reliable method. It removes the borrowing step that causes most manual errors.
Step 1: Convert both times to minutes since midnight
Step 2: Subtract
Step 3: Add a full day
Step 4: Convert back to hours and minutes
The shift ran 7 hours 45 minutes, which is 7.75 decimal hours for payroll
This is the single most useful table for anyone filling in a timesheet. Payroll multiplies decimal hours by your rate, so entering clock minutes by mistake quietly changes your pay.
| Minutes | Decimal Hours | Common Mistake |
|---|---|---|
| 5 min | 0.08 | Writing 0.05 |
| 10 min | 0.17 | Writing 0.10 |
| 15 min | 0.25 | Writing 0.15 |
| 20 min | 0.33 | Writing 0.20 |
| 30 min | 0.50 | Writing 0.30 |
| 40 min | 0.67 | Writing 0.40 |
| 45 min | 0.75 | Writing 0.45 |
| 50 min | 0.83 | Writing 0.50 |
Writing 7:30 as 7.30 rather than 7.50 understates the shift by 12 minutes. Over 20 shifts a month that is four hours of unpaid work. Always divide the minutes by 60 before entering a decimal figure.
Hourly workers and freelancers convert logged time into billable decimal hours. A quarter-hour rounding policy is common, but the underlying arithmetic still has to be right before any rounding is applied.
Scheduling software has to know whether a rest gap between shifts meets legal minimums. That means subtracting one clock time from another across a date boundary, which is exactly the midnight-crossing case above.
Working backwards from a deadline is a subtraction problem. If a roast needs 3 hours 20 minutes and must be served at 7:00 PM, it goes in at 3:40 PM. The add/subtract mode handles this directly.
To estimate elapsed time fast, count whole hours first, then handle the minutes. From 9:40 AM to 2:15 PM: 9:40 to 1:40 is four hours, and 1:40 to 2:15 is 35 minutes, giving 4 hours 35 minutes. Splitting the problem avoids borrowing entirely.
Most of the world uses the 24-hour clock for anything official, while the United States, Canada and a few other countries keep the 12-hour AM/PM system in daily life. Converting between them is where scheduling errors creep in, particularly around noon and midnight.
| 12-Hour | 24-Hour | Note |
|---|---|---|
| 12:00 AM | 00:00 | Midnight, start of the day |
| 1:00 AM | 01:00 | Same number |
| 11:59 AM | 11:59 | Last minute before noon |
| 12:00 PM | 12:00 | Noon, not midnight |
| 1:00 PM | 13:00 | Add 12 |
| 11:00 PM | 23:00 | Add 12 |
The genuine trap is 12:00 AM versus 12:00 PM. Midnight is 00:00 and noon is 12:00. Because so many people get this backwards, transport timetables and hospitals often write 23:59 or 00:01 to remove all doubt.
This calculator is provided for general informational purposes. For payroll, overtime or legal compliance questions, check your employer's policy and applicable labour law in your jurisdiction.