Add / Subtract Time
Add or subtract hours, minutes, and seconds from a time.
About this tool
Add or subtract an interval of hours, minutes, and seconds from a starting clock time. The tool converts everything to seconds, applies starting seconds ± (hours × 3,600 + minutes × 60 + seconds), and then wraps the result across a 24-hour day. That handles carryovers such as 75 minutes and makes midnight crossings visible. Start at 10:45 AM and add 1 hour 20 minutes to get 12:05 PM. Subtract 45 minutes from 12:15 AM and the result is 11:30 PM on the previous day. A movie beginning at 6:10 PM with a runtime of 2 hours 35 minutes should finish around 8:45 PM. Similar checks help with cooking stages, medication intervals, shift planning, airport connections, and exercise sessions. Enter the starting hour and minute, choose Add or Subtract, then fill in any combination of interval hours, minutes, and seconds. The starting-time control does not accept seconds, so it begins at :00; interval seconds are still supported. The result includes a day offset such as “Same day,” “+1 day,” or “-1 day.” It does not attach a calendar date or account for time-zone changes.
How to use
Choose the starting clock time in the HH:MM field; it begins with zero seconds.
Under "Operation," select "Add" or "Subtract," then enter the interval’s Hours, Minutes, and Seconds.
Press "Calculate" to see the resulting time and any day change.