Time Calculator
Add and subtract lengths of time in days, hours, minutes and seconds, with the carrying and borrowing done for you at 60 and at 24. Apply a span to a date and time to find where it lands, or type the whole sum as one expression. This page does time arithmetic; to measure the gap between two clock readings instead, use the Time Duration Calculator.
Empty fields count as zero. Carrying happens at 60 seconds, 60 minutes, and 24 hours.
Your total will appear here
Enter time values or an expression, then calculate to see the sum in days, hours, minutes, and seconds.
Carrying at 60, and Rolling Past Midnight
Time arithmetic is base 60 for minutes and seconds, and base 24 for hours, which is why doing it in your head goes wrong in a way decimal arithmetic does not.
Carrying. 2h 45m plus 1h 30m is not 3h 75m. Seventy-five minutes carries an hour, giving 4h 15m. The same happens at 60 seconds, and again at 24 hours, where a total rolls into a day.
Borrowing. Subtraction runs the other way. 3h 10m minus 1h 40m needs an hour broken into 60 minutes first: 2h 70m minus 1h 40m is 1h 30m.
Rolling past midnight. Adding a span to a clock time wraps at 24:00. Four hours and fifteen minutes after 22:30 is 02:45 the next day, and the day matters — a result that looks earlier than where you started has crossed a midnight. Subtracting works the same way in reverse, landing on the previous day. Use the date-and-time mode when you need the answer to carry its date rather than just a clock reading.
12-Hour and 24-Hour Notation
You can type either. The calculator accepts 1:45 PM and 13:45 as the same instant, and shows both forms in the result so there is nothing to convert in your head.
The 12-hour trap is midnight and noon. The hour before 1 AM is 12 AM, not 0 AM, and the hour before 1 PM is 12 PM. So 12:00 AM is midnight, the start of the day, and 12:00 PM is noon — the opposite of what many people assume, and the reason a deadline written “by 12 AM Friday” is genuinely ambiguous in practice even though it is not in principle.
24-hour notation has no such problem: 00:00 is midnight and 12:00 is noon, and every reading is unambiguous. It is worth using whenever the time is going into a contract, a rota or a log.
| 24-hour | 12-hour | |
|---|---|---|
| 00:00 | 12:00 AM | Midnight, start of the day |
| 12:00 | 12:00 PM | Noon |
| 13:45 | 1:45 PM | Afternoon |
| 23:59 | 11:59 PM | Last minute of the day |
Which time tool?
- Adding or subtracting a span — you are in the right place.
- Measuring between two clock times — “how long from 22:00 to 06:00?” — use the Time Duration Calculator.
- Totalling a week of shifts — use the Time Card Calculator.
- Whole days rather than hours — use the Date Calculator.
Which time tool should you use?
- Trying to measure the difference between two clock times? Use the Time Duration Calculator.
- Working with calendar dates? Use the Date Calculator.
Quick Answer
This is time arithmetic. It adds and subtracts spans of time in days, hours, minutes, and seconds, carrying at 60 and 24, and it can apply a span to a date and time. It does not measure the gap between two clock readings — that is what the Time Duration Calculator is for.
How It Works: Formula & Variables
Total = Σ (± values) · carry at 60s → 1m, 60m → 1h, 24h → 1d
- 1 day
- 24 hours · 1,440 minutes · 86,400 seconds.
- 1 hour
- 60 minutes · 3,600 seconds.
- 1 minute
- 60 seconds.
Values are added from the smallest unit up, carrying whenever a unit overflows.
Worked Examples
Example 1: Adding, with a carry
2h 45m + 1h 30m. The minutes total 75, which carries an hour, so the answer is 4h 15m — not the 3h 75m that straight addition suggests.
Example 2: Subtracting, with a borrow
3h 10m − 1h 40m. Forty minutes will not come out of ten, so an hour is broken into sixty first: 2h 70m − 1h 40m = 1h 30m.
Example 3: Rolling past midnight
A batch job starts at 22:30 and runs for 4h 15m. It finishes at 02:45 the following day. The clock reading alone would read as earlier than the start, which is the signal that a midnight has been crossed — use the date-and-time mode when the day needs to come with the answer.
Example 4: Mixed notation
Start at 1:45 PM and add 30 minutes: the result is 2:15 PM, shown also as 14:15. You can type either notation, and 13:45 and 1:45 PM are read as the same instant. Note that 12:00 AM is midnight and 12:00 PM is noon, which is the one pair worth checking before trusting a 12-hour reading.
Key Concepts
Time carries at 60, not 100: 1:30 plus 1:30 is 3:00, not 2:60. Minutes and seconds roll over at 60, which is the part manual math tends to get wrong.
Adding is not the same as measuring: This tool combines lengths of time. Finding how long sits between 9:34 and 11:03 is a duration question, handled by a different tool.
Blank fields mean zero: An empty box is treated as nothing to add, so you only fill in the units you actually have.
Common Mistakes
Adding time as if it were decimal: 1:30 plus 1:30 rolls over at 60, giving 3:00 rather than 2:60.
Confusing this with a duration tool: This calculator adds and subtracts spans; it does not read the gap between two clock times.
Misreading blank fields: An empty box counts as zero, not as "leave this part out of the math".
Frequently Asked Questions
Enter each length of time in the day, hour, minute, and second fields and the calculator adds them with proper carrying — 60 seconds roll into a minute, 60 minutes into an hour, and 24 hours into a day. Rows you leave blank simply count as zero.
Yes. Set a row to the minus sign and the calculator borrows across units where it needs to, so 1 hour 5 minutes minus 40 minutes correctly gives 25 minutes rather than a negative-looking result.
The "Add to date" tab takes a starting date and time, then adds or subtracts a span in days, hours, minutes, and seconds to give you a new date and time.
This tool adds and subtracts lengths of time, such as 2 hours plus 3 hours. It does not measure the gap between two clock readings — for that, use the Time Duration Calculator.
You can type a whole calculation in one line using values with d, h, m, or s joined by plus and minus signs, for example 1d 2h 3m 4s + 4h 5s − 2030s. The calculator reads it and returns the total.
There are 86,400 seconds in a day, which is 24 hours multiplied by 3,600 seconds per hour.
Related Calculators
Time Duration Calculator
Measure the difference between two clock times instead of adding up lengths of time.
Date Calculator
Work with calendar dates — the gap between two, or adding days, weeks, months, and years.
Hours Calculator
Turn a start and end time into hours worked, with break deduction and decimal hours.
Time Card Calculator
Add up a full week of in and out times, overtime, and gross pay.