Time duration:
find the hours and minutes between two times

What is time duration?

Time duration is the length of time that passes between a start and an end, such as a shift that begins at 09:45 and finishes at 13:20. It is an amount of time (3 hours 35 minutes), not a clock reading like 13:20.

You need it for work shifts, exam slots, train and flight journeys, phone calls, video lengths and billable hours. The method is always the same: put both times on the same clock, subtract, and write the answer in hours and minutes.

Hours and minutes are base-60 units, which is why 1 hour 30 minutes is not 1.30 hours. The safest habit is to work in minutes and convert back only at the end.

Time duration formula and 24-hour clock steps

1. 1Write both times on the 24-hour clock. Add 12 to PM hours (except 12 noon) and treat 12:xx AM as 00:xx.
2. 2Turn each time into minutes after midnight: hours × 60 plus minutes.
3. 3Subtract the start from the end. If the result is negative, add 1,440.
4. 4Divide the minutes by 60. The whole number is hours and the remainder is minutes.

Most errors in duration sums come from the 12-hour clock, not from the subtraction. A 24-hour time has no AM or PM, so a start of 11:45 PM and an end of 6:15 AM can no longer be confused with each other.

The rule is short. For AM, keep the hour as it is, except that 12 AM becomes 00. For PM, add 12 to the hour, except that 12 PM (noon) stays 12.

Once every time is in the last column, the rest of the job is one subtraction. That is also how a time duration calculator works internally.

Worked examples: same day and overnight

Start with a same-day case. A meeting runs from 9:45 AM to 1:20 PM.

Now an overnight shift. When the end time is earlier on the clock than the start time, the shift has crossed midnight and the subtraction goes negative. That negative number is your signal to add a day.

A quick check for overnight shifts: 22:30 to midnight is 1 h 30 min and midnight to 06:15 is 6 h 15 min. Together that is 7 h 45 min, matching the result.

Minutes to decimal hours chart

Payroll sheets and invoices often want decimal hours (7.75) rather than 7 h 45 min. Divide the minutes by 60 and add the result to the whole hours.

Values such as 10, 20 and 50 minutes repeat forever (0.1666…, 0.3333…, 0.8333…), so rounding each day can shift a weekly total by a few minutes. Keep totals in minutes until the final step.

To go the other way, multiply the decimal part by 60. For 7.75 hours, 0.75 × 60 = 45, so the answer is 7 h 45 min.

Adding durations, rounding and travel times

To total a week of shifts, convert each to minutes, add them, and convert once at the end. Adding the hours and minutes columns separately also works, but you must carry every 60 minutes into the hours column.

A raw duration is rarely the number you finally use. Employers and clients often round it, so check the rule that applies to you before you quote a figure.

Some businesses bill in blocks, for instance 15 minutes. A 3 h 35 min job is 215 minutes, and 215 ÷ 15 = 14.33, so it is billed as 15 blocks, which is 225 minutes or 3.75 hours. Others round to the nearest 5 or 10 minutes, or pay only whole minutes worked.

For travel, remember that the printed times on a ticket are local times. A train that leaves at 22:10 and arrives at 05:40 has a duration of 7 h 30 min, which you can check by splitting at midnight: 1 h 50 min before it and 5 h 40 min after.

For meetings and study plans, work backwards instead. Add the duration to the start time (09:45 plus 3 h 35 min) to get the end time of 13:20. The same minutes arithmetic works in both directions, which is useful when you know when something must finish and need to work out when to begin.

Mistakes people make when calculating time

• Reading 1.30 as one and a half hours. 1.30 hours is 1 h 18 min; 1 h 30 min is 1.50 hours.
• Forgetting to add 12 to PM times, or treating 12:15 AM as 12:15 instead of 00:15.
• Subtracting hours and minutes separately and leaving a negative minutes figure. Borrow 60 minutes instead: 4 h −25 min is 3 h 35 min.
• Ignoring the date. Clock times alone cannot tell you whether a trip took 7 hours or 31 hours.
• Mixing time zones. Convert both times to the same zone first; India uses one zone, so the clash usually shows up on international calls and flights.

If the gap runs across several days rather than hours, the guides on date differences and working days are the better fit. For the unit steps in this guide, use the hour to minute and minute to second converters on this page.