How the result time is calculated
The base time and the offset are both converted to minutes and added together. The result is taken modulo 1,440 (minutes in a day) to get the clock time, and how many full days were crossed is tracked separately.
- base hr / base min — starting time, 24h clock (0–23 / 0–59)
- add hr / add min — hours/minutes to add — negative to subtract
- total — combined minutes since midnight, before wrapping
- day shift — whole days crossed (negative = earlier day)
More detail
Crossing midnight in either direction
Adding enough time can push the result past 23:59 into the next day, and subtracting enough can push it before 00:00 into the previous day. The day shift output shows exactly how many days the result moved — e.g. 23:00 plus 2 hours gives 01:00 with a shift of +1 day, and 00:10 minus 20 minutes gives 23:50 with a shift of −1 day.
Practical tip. To subtract time instead of adding it, just enter a negative number in the "Add" hour or minute field — the result and day shift adjust automatically.
Frequently asked questions
What time is 3 hours 30 minutes after 09:00?
12:30, same day (day shift 0). Enter base 09:00 and add 3h 30m above to see it computed.
What time is 2 hours after 23:00?
01:00, with a day shift of +1 — since 23:00 + 2 hours crosses midnight, the result lands on the next calendar day.
How do I subtract time instead of adding it?
Enter a negative value in the "Add — hr" or "Add — min" field. For example, base 00:10 with add hr 0 and add min −20 gives 23:50 with a day shift of −1 (the previous day).
What does a day shift of −1 mean?
It means the result time falls on the calendar day before the base time — the offset you subtracted was large enough to cross back over midnight.
How is this different from a time duration calculator?
A time duration calculator takes two clock times and finds the gap between them; this calculator does the reverse — it takes one time plus an hour/minute offset and finds the resulting time.