What time will it be?
The add time calculator adds or subtracts hours and minutes from a time of day. It answers questions like “what time will it be in 8 hours?”, “what time was it 90 minutes ago?” or “if I start at 10:15 PM and it takes 7 hours 45 minutes, when do I finish?”. When the result passes midnight, it tells you whether it falls on the next day or the previous one.
The method
- Convert the start time to minutes after midnight: 8:00 AM is 480 minutes.
- Add or subtract the hours × 60 plus the minutes.
- Divide by 1,440, the minutes in a day: the quotient is the number of days moved, and the remainder is the clock time.
Worked example
Starting at 8:00 AM and adding 8 hours 45 minutes:
- 8:00 AM = 480 minutes.
- 8 h 45 min = 525 minutes; 480 + 525 = 1,005 minutes.
- 1,005 minutes = 16 hours 45 minutes, so the result is 4:45 PM the same day.
Starting at 6:00 PM and adding 8 hours gives 2:00 AM the next day: 1,080 + 480 = 1,560 minutes, one day and 120 minutes.
12-hour and 24-hour time
| 12-hour | 24-hour |
|---|---|
| 12:00 AM (midnight) | 00:00 |
| 6:30 AM | 06:30 |
| 12:00 PM (noon) | 12:00 |
| 4:45 PM | 16:45 |
| 11:59 PM | 23:59 |
The calculator shows times in the 12-hour format used in the US. Hospitals, the military and transport timetables use 24-hour time to avoid AM/PM mix-ups.
Common uses
- Medication: when to take the next dose, every 6 or 8 hours.
- Cooking: when a slow-cooker recipe or a brine will be ready.
- Travel: arrival time from a departure time and a trip length, in the same time zone. Add or subtract the time difference separately when crossing time zones.
- Work: the end of a shift from its start time and length.
- Parking and rentals: when a 2-hour meter or a 24-hour rental expires.
Large amounts of time
You can add more than 24 hours: 50 hours after 8:00 AM is 10:00 AM two days later. For periods counted in days, weeks or months, the date calculator is more convenient.