Time Addition, Subtraction and Conversion
Time uses a base-60 system for seconds and minutes and base-24 for hours — different from regular decimal arithmetic. When adding time, carry over when minutes reach 60 or seconds reach 60. When subtracting, borrow 60 seconds from minutes or 60 minutes from hours as needed.
Decimal Hours for Payroll
Payroll and billing systems often use decimal hours. Convert by dividing minutes by 60: 7 hours 30 minutes = 7.5 hours, 7 hours 20 minutes = 7.333 hours. Common fractions: 15 min = 0.25h, 30 min = 0.5h, 45 min = 0.75h, 10 min = 0.167h, 40 min = 0.667h.
Calculating Shift Duration
For simple day shifts, subtract start from end. For shifts crossing midnight — say 10:00 PM to 6:00 AM — add 24 hours to the end time: 30:00 − 22:00 = 8 hours. Our Duration tab handles this automatically.
Frequently Asked Questions
How do I add hours and minutes?
Add hours and minutes separately. If minutes exceed 60, carry over: 3h 45m + 2h 30m = 5h 75m = 6h 15m. Our calculator handles carries automatically.
How many minutes are in a day?
1,440 minutes (24 × 60). There are 86,400 seconds in a day, 168 hours in a week, and 10,080 minutes in a week.
How do I convert hours to decimal?
Divide minutes by 60 and add to hours. 3 hours 45 minutes = 3 + 45/60 = 3.75 hours. Used for timesheets: 7h 30m = 7.5h. At $25/hr, 7.5 × $25 = $187.50.
How do I calculate hours worked?
Subtract start time from end time. 9:15 AM to 5:45 PM = 8h 30m. Subtract any unpaid breaks. If crossing midnight, add 24 hours to end time before subtracting.
What is the difference between 12-hour and 24-hour time?
12-hour uses AM/PM (1–12). 24-hour uses 0–23: midnight = 00:00, noon = 12:00, 1 PM = 13:00, 11 PM = 23:00. 24-hour time eliminates AM/PM ambiguity used in schedules and military contexts.