Time Calculator
Add and subtract time, measure durations between two times, and convert between seconds, minutes, hours, days and weeks.
Calculate
If the end is earlier than the start, it's counted as overnight (next day).
Define your own unit by how many seconds it lasts.
How to Use the Time Calculator
Three modes cover every time question. Add / Subtract does time arithmetic with natural input — type 2h 45m, 1:30:00, or 90m and the parser understands all of them. Duration measures elapsed time between two moments (pick date + time for each); if the end comes before the start, it's counted as overnight automatically. Convert flips one value across seconds, minutes, hours, days, and weeks — with a custom-unit option if you define time your own way (a "work shift" of 8 hours, say).
Adding Time Values
The method is always the same: convert to the smallest unit, do the arithmetic, convert back.
Minutes roll over at 60, which is why mental time math feels hard — our brains want base 10. The calculator removes the friction: paste durations in whatever format you have and get every unit back at once (4h 15m = 255 minutes = 15,300 seconds = 4.25 hours).
Finding Duration Between Two Times
Subtract start from end. The two classic pitfalls:
- Overnight: 10:00 PM → 6:00 AM looks "backwards" but means 8 hours — the calculator adds a day automatically and tells you it did.
- AM/PM confusion: 12:00 AM is midnight, 12:00 PM is noon. For durations spanning noon or midnight, the datetime pickers remove all ambiguity.
For payroll-style totals across a whole week (with breaks and overtime), the Hours Calculator is the better tool — this one is for quick arithmetic.
Worked Example: 9:15 AM to 5:45 PM
A standard workday, no lunch break counted
Step 1: Convert to 24-hour: 9:15 → 09:15, 5:45 PM → 17:45.
Step 2: Subtract: 17:45 − 9:15 = 8 hours 30 minutes.
In other units: 510 minutes · 30,600 seconds · 8.5 decimal hours.
Subtract a 30-minute lunch and you get the paid 8.0 hours — the Hours Calculator does that version with one extra field.
12-Hour vs 24-Hour Formats
The 12-hour clock (with AM/PM) dominates everyday life in the US; the 24-hour clock dominates schedules, aviation, medicine, and most of the world. Converting is mechanical: PM hours add 12 (5:30 PM → 17:30), except 12 PM which stays 12:00 and 12 AM which becomes 00:00. When precision matters — shifts, flights, medication — the 24-hour format earns its keep by making 17:30 unambiguous. Both work in the duration pickers above.
My saved numbers reuse them in any calculator
Save a number once — like your rent or hourly rate — then just type its name instead of the number, in any calculator here. You can also type formulas like 5000 * 1.1 right into any box.
Saved only in this browser — nothing is sent to us.
Frequently Asked Questions
How do you add time values?
Convert both to the same unit (usually minutes or seconds), add, then convert back. 2h 45m + 1h 30m = 165 + 90 = 255 minutes = 4h 15m. The calculator accepts natural input like "2h 45m" directly.
How do I calculate elapsed time?
Subtract the start from the end: 9:15 AM to 5:45 PM is 8 hours 30 minutes. If the end is earlier than the start, the calculator assumes the next day (overnight).
What is 2h 45m + 1h 30m?
4 hours 15 minutes. In minutes: 165 + 90 = 255. In decimal hours: 4.25.
How do I convert minutes to hours?
Divide by 60: 90 minutes = 1.5 hours. Use Convert mode above to flip between seconds, minutes, hours, days and weeks instantly.
What is the difference between 12-hour and 24-hour clock?
The 12-hour clock uses AM/PM (9:00 AM, 5:30 PM); the 24-hour clock counts 00:00–23:59 (09:00, 17:30). The 24-hour format removes AM/PM ambiguity — 17:30 can only mean afternoon.