Minutes-since-midnight method
The simplest way to add time is to convert the base time into total minutes, add the duration (in minutes), then convert back to hours and minutes.
Clock times like 09:00 are easier to compute with if you treat them as minutes since midnight. For example, 09:00 is 9 x 60 = 540 minutes.
Durations also convert cleanly: 2h 30m is 2 x 60 + 30 = 150 minutes.
Adding is straightforward: 540 + 150 = 690 minutes. Convert back: 690 / 60 = 11 hours, 690 % 60 = 30 minutes. Result: 11:30.
- Base: 09:00 (540 min)
- Duration: +2:30 (150 min)
- Total: 690 min = 11:30
Try it: Add/Subtract time
Convert both the base time and the duration into minutes, then add/subtract.
Crossing midnight (day shift)
If the result goes past 24:00 (or below 00:00), you wrap around and track how many days you moved (day shift).
If you add time to a late-night clock time, you can end up on the next day. Similarly, subtracting from an early morning time can go to the previous day.
Because a clock time has no date, we show day shift as +1, -1, etc. It tells you how many midnights you crossed.
Example: 23:30 (1410 min) + 2:00 (120 min) = 1530 min. Since 1530 > 1440 (24 hours), we subtract 1440 and get 90 min = 01:30, with +1 day shift.
- Base: 23:30 (1410 min)
- Duration: +2:00 (120 min)
- Total: 1530 min
- 1530 - 1440 = 90 min = 01:30 (+1 day)
Try it: Crossing midnight
When you cross midnight, the clock wraps but day shift records the overflow.
Add vs subtract (quick mental checks)
Use subtract when you want to go backwards from a time (e.g., "2 hours before 01:00").
Add: 09:00 + 0:30 = 09:30 (moves forward in time).
Subtract: 01:00 - 2:00 = 23:00 (previous day). The calculation is 60 - 120 = -60. Wrap by adding 1440: -60 + 1440 = 1380 min = 23:00, and day shift is -1.
If your result looks "off", check whether you used add vs subtract and whether midnight was crossed.
- Base: 01:00 (60 min)
- Duration: -2:00 (120 min)
- 60 - 120 = -60 min
- -60 + 1440 = 1380 min = 23:00 (-1 day)
Try it: Subtract a duration
Subtracting from early hours often moves to the previous day.
Duration input format
The calculator accepts flexible duration formats - including large hour values.
The primary format is H:MM (e.g., 2:30 for 2 hours 30 minutes). Hours can be any number - 50, 500, or even 20000.
If you type only digits (like "50"), it becomes hours: 50 → 50:00 (50 hours). The field formats on blur.
For minutes-only durations, use 0:45 (45 minutes). For very long durations, just type the hours: 2000 → 2000:00.
- 2:30 = 2 hours 30 minutes
- 50 → 50:00 (50 hours)
- 2000:30 = 2000 hours 30 minutes
- 0:45 = 45 minutes
Try it: Duration formats
Type hours directly (digits become H:00) or use H:MM format.
Real-world use cases
Time arithmetic appears in many everyday scenarios.
Flight arrivals: Departure 11:00 PM + 14-hour flight = 1:00 PM next day (+1 day). Know when to arrange pickup.
Work shifts: Start at 10:00 PM, work 8 hours = end at 6:00 AM next day. Overnight shift planning.
Cooking: Put the roast in at 2:30 PM, cook for 3h 45m = done at 6:15 PM. Never miss the timer.
Travel planning: Leave at 9:00 AM, drive 5h 30m = arrive at 2:30 PM. Factor in breaks by adding more time.
Meeting scheduling: Meeting at 4:00 PM lasts 1h 30m = ends at 5:30 PM. Plan your next appointment.
- Depart: Monday 11:00 PM
- Flight: 14:00 (14 hours)
- Arrive: Tuesday 1:00 PM (+1 day)
Try it: Plan a scenario
From flights to cooking, time arithmetic helps planning.
Auto-detected time and day
The calculator auto-fills your current time and weekday, making quick calculations effortless.
When you load the calculator, it automatically fills in the current time and today's day of week from your device.
This means you can instantly calculate "what time will it be in 3 hours?" without entering your current time.
Day shift tells you how many midnights you crossed. Combined with the base weekday, the calculator computes the resulting weekday.
Example: Monday 23:30 + 2:00 = Tuesday 01:30. The +1 day shift moves Monday to Tuesday.
You can change the base time and day manually if calculating for a different moment.
- Base: Friday 23:00 (auto-filled)
- Duration: +3:00
- Result: Saturday 02:00 (+1 day)
Related: Time Duration
Current time + day auto-detected = instant calculations.