⏲️ Time Duration Calculator
Add or subtract hours and minutes from any start time. Get the result in both standard 12-hour and military 24-hour format. Midnight crossover is handled automatically.
Time Duration Calculator
Common Examples
| Start Time | Operation | Result (Standard) | Military |
|---|---|---|---|
| 2:30 PM | + 3h 45m | 6:15 PM | 1815 |
| 11:15 PM | + 2h 0m | 1:15 AM (next day) | 0115 |
| 8:00 AM | + 8h 0m | 4:00 PM | 1600 |
| 12:00 AM | + 6h 30m | 6:30 AM | 0630 |
| 3:00 PM | − 5h 0m | 10:00 AM | 1000 |
| 1:00 AM | − 3h 0m | 10:00 PM (prev. day) | 2200 |
How It Works
The calculator converts the start time to minutes since midnight (a plain number from 0 to 1,439), adds or subtracts the duration in minutes, then converts the result back to a readable time. This approach eliminates AM/PM confusion and handles midnight crossover automatically.
If the result exceeds 1,440 minutes (24 hours), it wraps to the next day and displays “Next day.” If the result falls below 0, it wraps to the previous day and displays “Previous day.” Both the 12-hour standard time and the 4-digit military time are shown for every result.
Frequently Asked Questions
What is 2:30 PM plus 3 hours 45 minutes?
2:30 PM + 3 hours 45 minutes = 6:15 PM (military time 1815). To verify manually: 2:30 PM = 870 minutes since midnight. 870 + 225 = 1,095 minutes. 1,095 ÷ 60 = 18 hours 15 minutes = 6:15 PM.
What is 11:15 PM plus 2 hours?
11:15 PM + 2 hours = 1:15 AM the next day (military time 0115). 11:15 PM = 1,395 minutes. 1,395 + 120 = 1,515 minutes. 1,515 − 1,440 = 75 minutes = 1:15 AM, crossing into the next day.
How do I add hours and minutes manually?
Convert the start time to minutes since midnight (multiply hours by 60 and add the minutes). Add the duration in minutes. If the result exceeds 1,440, subtract 1,440 and note it is the next day. Convert back by dividing by 60 for hours and using the remainder for minutes.
How many minutes are in a day?
There are 1,440 minutes in a day (24 hours × 60 minutes per hour). This is the modulo used when the result wraps past midnight.
Does this handle AM/PM correctly?
Yes. The calculator converts AM/PM input to a 24-hour value internally (so 12:00 AM = 0, 12:00 PM = 720, 11:59 PM = 1,439), performs the arithmetic, then converts back. This avoids all AM/PM ambiguity in the calculation.
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Results are provided for general informational purposes. Time zone and daylight saving adjustments are not accounted for. Read our full disclaimer.