Time Calculator
Time difference, add/subtract duration, and convert hours ↔ minutes ↔ seconds.
Time calculator
Duration, time difference, and unit conversion.
Compute time between two times or dates, add/subtract time, and convert between hours, minutes, and seconds.
- Duration between two clock times in hours, minutes, and seconds.E.g. 09:00 to 17:30 is 8 hours 30 minutes.
- Date-difference mode gives the number of days between two dates.E.g. 2025-01-01 to 2025-03-01 is 59 days.
- UTC (Coordinated Universal Time)
- UTC is the primary time standard. Local times are often given as UTC offset (e.g. KST = UTC+9).
- Duration
- Duration is the length of time between two instants, used for work hours, study time, travel time, etc.
Where time calculations go wrong
Time runs in base 60, not base 10, so treating it like ordinary addition produces wrong answers. Crossing midnight and mixing up clock times with durations account for most of the rest.
Working in base 60
One hour 45 minutes plus 30 minutes is 2 hours 15 minutes, not 1 hour 75 minutes. Minutes carry into hours once they reach 60.
When a calculation gets awkward, convert everything to minutes or seconds, do the arithmetic, then convert back. 1h45m = 105 minutes, 105 + 30 = 135, and 135 ÷ 60 = 2h15m.
Clock times are not durations
'3pm' is a point in time; '3 hours' is a length of time. You can add a duration to a clock time (3pm + 3 hours = 6pm), but adding two clock times together rarely means anything.
Subtracting two clock times does mean something: the result is a duration. 6pm − 3pm = 3 hours.
Crossing midnight
A shift from 22:00 to 06:00 is 8 hours, not 06 − 22 = −16. When the end time is smaller than the start time the clock has rolled past midnight, so add 24 hours.
Treat 06:00 as 30:00, then 30 − 22 = 8 hours. This is the single most common error in night-shift and late-opening-hours calculations.
12-hour and 24-hour clocks
12am is midnight (00:00) and 12pm is noon (12:00). The 12 o'clock labels run counter to intuition, which is why they cause so much confusion in schedules and contracts.
The 24-hour clock avoids the problem. Note that 00:00 and 24:00 refer to the same instant but belong to different days.
Paid hours versus hours on site
Clocking in at 09:00 and out at 18:00 is 9 hours on site, but subtracting an hour for lunch leaves 8 paid hours.
Break rules vary by country and contract, and unpaid breaks are normally excluded from working time. When producing hours for payroll, check whether breaks have already been deducted.
| Unit | Equivalent |
|---|---|
| 1 hour | 60 minutes · 3,600 seconds |
| 1 day | 24 hours · 1,440 minutes · 86,400 seconds |
| 1 week | 7 days · 168 hours |
| 15 minutes | 0.25 hours |
| 20 minutes | 0.333… hours |
| 45 minutes | 0.75 hours |
Frequently asked questions
- How long is a shift from 22:00 to 06:00?
- 8 hours. When the end time is earlier than the start, add 24 hours: 6 + 24 = 30, and 30 − 22 = 8.
- What is 1 hour 45 minutes plus 30 minutes?
- 2 hours 15 minutes. Minutes carry at 60. Converting to minutes first (105 + 30 = 135) makes it harder to slip up.
- How many hours is 20 minutes?
- 0.333… hours, since 20 does not divide evenly into 60. For payroll, agree on a rounding convention in advance.
- Is 12pm noon or midnight?
- 12pm is noon and 12am is midnight. Because this is so easily misread, the 24-hour clock is safer for anything contractual.
- Is 09:00 to 18:00 eight hours or nine?
- Nine hours on site, eight once an unpaid hour of break is deducted. Check which figure your payroll expects.