Time Calculator
Add or subtract hours, minutes, and seconds from a starting time. Cross midnight and the result tells you which day you landed on.
How it works
The calculator converts your start time to a total number of seconds since midnight, then adds or subtracts the hours, minutes, and seconds you entered. The time-of-day result is the remainder after dividing by 86,400 (the number of seconds in a day), and the day shift is how many whole days fit into the total. So 23:00 plus 3 hours is 93,600 seconds — one full day plus 7,200 seconds — which reads as 02:00 with a +1 day badge. Everything runs in your browser, so results update as you type.
Worked examples
- 14:30 + 2 h 45 m → 17:15, same day.
- 23:00 + 3 h → 02:00, +1 day.
- 00:30 − 1 h → 23:30, −1 day.
- 08:15 + 36 h → 20:15, +1 day (24 h for the day shift, 12 h left over).
Edge cases
- Crossing midnight never loses a day: the day-shift badge counts every full 24-hour cycle, positive or negative.
- Very large amounts (e.g. 1,000 hours) wrap correctly; the badge shows the total day shift, not just "next day".
- Empty fields are treated as zero, so you can add just minutes without touching hours.
- Minutes or seconds above 59 are accepted and carried over automatically — 90 minutes is the same as 1 hour 30 minutes.
Frequently asked questions
What happens when the result crosses midnight?
The calculator keeps the clock reading in 24-hour form and shows the day shift next to it. For example, starting at 23:00 and adding 3 hours gives 02:00 with a "+1 day" badge; starting at 00:30 and subtracting 1 hour gives 23:30 with a "−1 day" badge. The time of day always stays between 00:00:00 and 23:59:59.
Can I add or subtract more than 24 hours?
Yes. Enter any number of hours — 36 hours, 100 hours, whatever you need. The result wraps around the clock as many times as required and the day-shift badge tells you how many days forward or backward you landed.
Does this calculator account for time zones or daylight saving?
No. It performs pure clock arithmetic on a single 24-hour dial, independent of any time zone. If you need to convert a moment between zones — where a DST transition could make a day 23 or 25 hours long — use the Time Zone Converter instead.
How is this different from the Add / Subtract Dates tool?
The Add / Subtract Dates tool moves a calendar date by whole days, weeks, or months and lands on a new date. This tool moves a time of day by hours, minutes, and seconds and stays on the clock face. Use this one for shift lengths, travel durations, and elapsed times; use the other for deadline dates.
Can I use this to calculate shift or work durations?
Yes — that is one of its most common uses. Enter your shift start time, add the hours and minutes worked, and you get the end time. For overnight shifts the day-shift badge shows you crossed into the next day, e.g. 22:00 + 8 hours = 06:00 (+1 day).
Related tools
All calculations run in your browser. No data leaves your device.