Duration is not a time of day
“3 hours 20 minutes” can be added directly. “15:40” is a clock reading and needs a start or finish context. Use Between times for clock readings.
Add or Subtract Hours, Minutes and Seconds
Combine two durations or find the difference between them without converting minutes into misleading decimal values first.
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Useful guidance
Accurate duration arithmetic
Minutes and seconds use base 60 rather than base 100. The calculator normalises both durations before adding or subtracting them, then presents a readable result and decimal hours.
Add durations2 hr 45 min + 1 hr 30 min4 hr 15 min
Subtract durations8 hr − 1 hr 20 min6 hr 40 min
Include seconds1:10:45 + 0:05:301:16:15
Add and subtract durations without decimal-time mistakes
Hours, minutes and seconds use base 60. Add like units, carry every 60 seconds into one minute and every 60 minutes into one hour. For subtraction, borrow one hour as 60 minutes or one minute as 60 seconds when required.
| Problem | Working | Answer |
|---|---|---|
| 2 hr 45 min + 1 hr 30 min | 3 hr + 75 min | 4 hr 15 min |
| 6 hr 10 min − 2 hr 45 min | 5 hr 70 min − 2 hr 45 min | 3 hr 25 min |
| 1:20:50 + 0:45:25 | 1 hr 65 min 75 sec | 2:06:15 |
Decimal conversion comes last
Convert the finished result only when needed. Fifteen minutes is 0.25 hour, 30 minutes is 0.50, and 45 minutes is 0.75—not 0.15, 0.30 or 0.45.
Negative results need context
If the amount being subtracted is larger, the mathematical result is negative. Check whether the real task should instead wrap into another day or represent remaining time.
Useful cases include project totals, training time, travel, media duration and accumulated overtime. Keep units explicit so the result remains understandable when copied elsewhere.