Time Calculator

How to use the time calculator

Enter the first duration in days, hours, minutes and seconds, choose Add or Subtract, then enter the second duration. The answer appears in four formats: a readable breakdown (for example 4h 16m 15s), clock-style hh:mm:ss, decimal hours, and total minutes and seconds. You can leave any field at zero, and values larger than the normal range are fine — typing 90 minutes is the same as 1 hour 30 minutes, and the calculator normalises the result for you.

This makes it easy to total running splits, video edit lengths, flight legs, cooking times, study sessions, timesheet entries or audio tracks without doing base-60 arithmetic in your head.

Why time arithmetic is tricky

Ordinary numbers are base 10, but time is mixed-base: 60 seconds make a minute, 60 minutes make an hour and 24 hours make a day. Adding 45 minutes to 30 minutes gives 75 minutes, which must be "carried" into 1 hour 15 minutes. The safest method — and the one this calculator uses — is to convert everything to a single unit, do the maths, and convert back.

To convert back, divide by 86,400 for days, take the remainder and divide by 3,600 for hours, then by 60 for minutes; what is left is seconds.

Worked example

Add 2 h 45 min 30 s and 1 h 30 min 45 s (the default values):

1. Time 1 = 2 × 3,600 + 45 × 60 + 30 = 9,930 seconds.
2. Time 2 = 1 × 3,600 + 30 × 60 + 45 = 5,445 seconds.
3. Sum = 15,375 seconds.
4. 15,375 ÷ 3,600 = 4 hours remainder 975 s; 975 ÷ 60 = 16 minutes remainder 15 s.

The answer is 4 h 16 min 15 s, or 4.2708 decimal hours. Subtracting instead gives 4,485 seconds = 1 h 14 min 45 s.

Decimal hours vs hours and minutes

Payroll and billing systems often use decimal hours, where 7.5 hours means 7 hours 30 minutes — not 7 hours 50 minutes. To convert minutes to a decimal, divide by 60: 15 min = 0.25 h, 20 min = 0.333 h, 45 min = 0.75 h. To go the other way, multiply the decimal part by 60: 0.4 h × 60 = 24 minutes.

If you are totalling a whole week of start and finish times, the hours calculator handles breaks, overnight shifts and pay for you. For running, the pace calculator turns a finish time into pace per kilometre or mile.

Tips for accurate time sums

• When adding many durations, add them two at a time: put the running total in time 1 and the next item in time 2.
• A negative result simply means the second time is longer — useful for finding how far behind a target you are.
• For the time between two clock times or dates (for example 22:30 to 06:15), use the hours calculator or the days between dates calculator instead.
• Fractions of a second are supported, so you can enter race splits such as 12.37 seconds.