Calculated using standard mathematical and industry formulas.
To calculate elapsed time, convert all durations into total seconds (1 hour = 3,600 seconds; 1 minute = 60 seconds), perform arithmetic addition or subtraction, and convert back using modulo 60 division. There are exactly 168 hours in a standard 7-day week. This tool handles multi-interval time cards, decimal payroll hours, and 24-hour time math.
How to use this calculator?
Select whether you want to add or subtract two time durations.
Enter the hours, minutes, and seconds for the first time duration.
Enter the hours, minutes, and seconds for the second time duration.
Read your combined total duration formatted as HH:MM:SS, decimal hours, total minutes, and total seconds.
Formula & calculation method
Base-60 Sexagesimal Conversion Method
Total Seconds = (H × 3600) + (M × 60) + S; Result Hours = ⌊Total Seconds / 3600⌋; Result Minutes = ⌊(Total Seconds % 3600) / 60⌋; Result Seconds = Total Seconds % 60; Decimal Hours = H + (M / 60) + (S / 3600)
To convert minutes to decimal hours, divide the number of minutes by 60 (e.g. 45 min ÷ 60 = 0.75 hours).
Adding time durations is essential for flight planning, audio/video editing tracks, athletic splits, and work timesheets.
How to interpret your results?
Decimal Hours vs. Clock Minutes (HH:MM)
In payroll accounting, clock minutes are converted to decimal hours: 15 min = 0.25 hrs, 30 min = 0.50 hrs, and 45 min = 0.75 hrs. A shift of 7 hours and 42 minutes equals 7.70 decimal hours.
12-Hour vs. 24-Hour (Military) Time
Military and international systems count continuous hours from 00:00 to 23:59 without AM/PM ambiguity. To convert afternoon PM hours, add 12 (e.g., 5:00 PM = 17:00).
Expert advice & guidance
💡 Payroll timesheet tip: When tracking billable consulting or freelance hours, always round to the nearest 0.1 hour (6 minutes) or 0.25 hour (15 minutes) to ensure standardized invoicing and seamless payroll export.
Frequently asked questions
How many hours are in a week and how many hours in 2 weeks?
There are exactly 168 hours in a standard 7-day week (7 days × 24 hours). In a two-week period (a fortnight or bi-weekly pay cycle), there are 336 hours. A typical full-time work week consists of 40 working hours, leaving 128 non-working hours.
How many seconds are in an hour and how many seconds in a minute?
There are exactly 3,600 seconds in one hour (60 minutes × 60 seconds). There are 60 seconds in one minute, and 86,400 seconds in a 24-hour day. In 8 hours (a full workday), there are 28,800 seconds.
How many days is 72 hours and how long is 72 hours?
Exactly 72 hours equals 3 full days (72 ÷ 24 = 3). For comparison: 24 hours is 1 day, 48 hours is 2 days, 96 hours is 4 days, 120 hours is 5 days, and 168 hours is 1 full week.
How long is 90 minutes and how long is 120 minutes in hours?
A duration of 90 minutes is equal to 1 hour and 30 minutes (1.5 hours). A duration of 120 minutes equals exactly 2 full hours (120 ÷ 60 = 2). Similarly, 45 minutes is 0.75 hours, and 150 minutes is 2.5 hours.
What time is it in military time (1700, 1800, 1600)?
In military time (24-hour clock): 1600 is 4:00 PM, 1700 is 5:00 PM, 1800 is 6:00 PM, 1900 is 7:00 PM, 2000 is 8:00 PM, and 0000 (or 2400) is midnight. Subtract 1200 from numbers 1300 and higher to find standard 12-hour PM time.
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