Add or subtract hours, minutes, and seconds. Convert between time units instantly.
Time uses a base-60 (sexagesimal) system inherited from ancient Babylonian mathematics: 60 seconds in a minute, 60 minutes in an hour, and 24 hours in a day. This makes time arithmetic trickier than standard decimal math. Adding 2 hours 45 minutes to 1 hour 30 minutes gives 3 hours 75 minutes, which must be converted to 4 hours 15 minutes because 75 minutes exceeds 60. This calculator handles all the carrying and borrowing automatically.
The calculator has three modes. Add/Subtract combines two time durations (e.g., adding travel segments or subtracting a break from total work time). Convert translates a time value between seconds, minutes, hours, days, and weeks. Elapsed Time finds the duration between a start time and end time using a 12-hour clock with AM/PM. All modes compute results instantly as you type.
Decimal hours to hours and minutes: multiply the decimal portion by 60. For example, 3.75 hours equals 3 hours and 45 minutes (0.75 x 60 = 45). Going the other direction, 2 hours 20 minutes in decimal is 2 + 20/60 = 2.333 hours. Payroll and billing systems often require decimal hours, while people naturally think in hours and minutes, making this conversion one of the most common time calculation needs.
The Date Difference Calculator handles calculations spanning days, months, and years, while this tool focuses on hours, minutes, and seconds within a single day or duration.
Work hours: Tracking hours worked for timesheets and payroll requires adding multiple time segments and subtracting breaks. An 8-hour workday from 8:30 AM to 5:00 PM with a 30-minute lunch is 8 hours total, or 7.5 hours of paid work if lunch is unpaid.
Cooking: Recipes often require adding preparation time, cooking time, and resting time. A recipe with 20 minutes prep, 1 hour 15 minutes baking, and 10 minutes cooling totals 1 hour 45 minutes from start to table.
Travel: Flight itineraries, layovers, and drive times all involve adding and subtracting time segments. A flight departing at 2:45 PM with a duration of 3 hours 20 minutes arrives at 6:05 PM local time (before time zone adjustments). The Time Zone Converter handles cross-zone calculations.
Exercise: Tracking workout duration, rest intervals, and total training time. The Pace Calculator converts between time and distance for runners.
The 60-minute hour and 60-second minute originate from the Babylonian base-60 number system, which dates to approximately 1800 BCE. The Babylonians chose base 60 because it is divisible by many factors (1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60), making fractions easy to express. The 24-hour day comes from ancient Egypt, which divided daylight and nighttime into 12 hours each based on the rising of specific star groups (decans). The second was formally defined in 1967 as 9,192,631,770 oscillations of a cesium-133 atom, making it one of the most precisely defined units in science.
The 24-hour clock (also called military time) eliminates AM/PM ambiguity. Hours run from 00:00 (midnight) to 23:59 (11:59 PM). To convert from 12-hour to 24-hour: AM hours stay the same (except 12 AM becomes 00:00), PM hours add 12 (1 PM becomes 13:00, 2 PM becomes 14:00, through 11 PM becoming 23:00), and 12 PM stays as 12:00. Aviation, military, healthcare, and most countries outside the United States use 24-hour time as the standard to avoid confusion between AM and PM.