What is a Time Calculator?
A time calculator performs arithmetic on hours, minutes, and seconds. It has two primary modes: adding or subtracting time durations (e.g., how long is 2h 45m + 1h 30m?) and finding the duration between two clock times (e.g., how long from 9:00 AM to 5:30 PM?). Both modes are essential for tracking work hours, planning schedules, calculating travel time, and solving school math problems.
How Does the Time Calculator Work?
The calculator converts all time values to seconds, performs the arithmetic in that single unit, then converts the result back to hours, minutes, and seconds. This approach handles edge cases like minute overflow (where adding 45m + 30m = 75m = 1h 15m) and overnight durations automatically. Results are shown in HH:MM:SS format, decimal hours, total minutes, and total seconds.
Formula Used
Convert to seconds: total_seconds = hours × 3600 + minutes × 60 + seconds
Add/Subtract: result_seconds = time1_seconds ± time2_seconds
Convert back: H = result ÷ 3600; M = (result mod 3600) ÷ 60; S = result mod 60
Decimal hours: result_seconds ÷ 3600
Time difference: Convert both clock times to seconds from midnight (accounting for AM/PM), subtract start from end, handle overnight (add 86400 if end < start)
Benefits of Using a Time Calculator
- Avoids manual error when carrying minutes and seconds across hours
- Shows decimal hours for easy payroll and timesheet calculations
- Handles AM/PM conversion in time difference mode
- Shows total in multiple units (seconds, minutes, hours) for flexibility
- Instant results — no manual arithmetic required
Frequently Asked Questions
How do I add hours and minutes together?
Convert to seconds, sum, convert back. For 2h 45m + 1h 30m: (2×3600+45×60) + (1×3600+30×60) = 9900 + 5400 = 15300 seconds = 4h 15m 0s.
How do I find the duration between two times?
Convert both to seconds from midnight, subtract. For 9:00 AM to 5:30 PM: 32400 to 63000 seconds → 30600 seconds difference = 8h 30m.
How many seconds are in a day?
86,400 seconds (24 × 60 × 60). One hour = 3,600 seconds. One minute = 60 seconds. One week = 604,800 seconds.
How do I calculate hours worked between two times?
Use the "Time Difference" mode. Enter start time and end time. The calculator shows total hours worked in both HH:MM:SS and decimal format (e.g., 8.5 hours) for payroll use.
How do I convert time to decimal hours?
Decimal hours = hours + (minutes ÷ 60) + (seconds ÷ 3600). Example: 7h 45m = 7 + 45/60 = 7.75 decimal hours. The calculator shows this automatically.
What happens when adding time crosses midnight?
Durations over 24 hours are shown as-is (e.g., 26h 30m). For clock time differences that cross midnight, the calculator detects overnight scenarios and adds 24 hours to give the correct duration.
How do I subtract time?
Use the Subtract mode. Convert both times to seconds and subtract. If the result is negative (subtracting more than available), the result is shown as a negative duration.
Can this calculator handle multiple time additions?
Add two at a time: first add durations 1+2, then use the result as input for duration 3, and so on. For complex multi-entry time sheets, a spreadsheet may be more efficient.