Time Calculator

Time math is deceptively tricky.

Adding 2 hours and 45 minutes to 3 hours and 30 minutes does not work the same way as adding regular numbers because time uses base 60 (60 minutes per hour, 60 seconds per minute) instead of base 10. This time calculator handles the base-60 arithmetic for you, making it simple to add, subtract, multiply, and convert time values.

Enter time values in hours, minutes, and seconds, and the tool performs the calculation correctly, carrying over 60 seconds into a minute and 60 minutes into an hour. It also converts time between formats, showing results in hours and minutes, total minutes, total seconds, and decimal hours, which is useful for timesheet calculations where employers need hours expressed as decimals.

Whether you are totaling up shift durations for a timesheet, calculating how long a multi-leg journey takes, figuring out the total runtime of a playlist or video series, or subtracting a start time from an end time to find a duration, this tool handles the base-60 math that trips people up.

How Time Arithmetic Works

The challenge with time math is that it operates in base 60 rather than the base 10 system we use for regular numbers. When you add 45 minutes to 30 minutes, the result is not 75 minutes in the same way that 45 + 30 = 75 in regular math. Instead, 75 minutes must be converted to 1 hour and 15 minutes.

Addition rules:

  1. Add seconds to seconds, minutes to minutes, hours to hours.
  2. If the seconds total is 60 or more, subtract 60 from seconds and add 1 to minutes.
  3. If the minutes total is 60 or more, subtract 60 from minutes and add 1 to hours.

Example: Add 2:45:30 (2 hours, 45 minutes, 30 seconds) to 1:25:45 (1 hour, 25 minutes, 45 seconds).

  • Seconds: 30 + 45 = 75. Subtract 60, carry 1. Seconds = 15, carry 1 minute.
  • Minutes: 45 + 25 + 1 (carry) = 71. Subtract 60, carry 1. Minutes = 11, carry 1 hour.
  • Hours: 2 + 1 + 1 (carry) = 4.
  • Result: 4:11:15

Subtraction follows the reverse process. If you need to subtract a larger number of seconds from a smaller number, borrow 60 seconds from the minutes column (reducing minutes by 1). If minutes go negative, borrow 60 minutes from the hours column.

Adding Multiple Time Values

One of the most practical uses for a time calculator is adding up multiple time durations. This comes up when totaling shift hours for a paycheck, calculating the total runtime of episodes in a TV season, or adding up segments of a workout.

Example: Adding shift hours for a week.

  • Monday: 8:15
  • Tuesday: 7:45
  • Wednesday: 8:30
  • Thursday: 8:00
  • Friday: 7:30

To add these manually, you would need to handle the carry-over from minutes to hours each time the minutes exceed 60. The calculator handles this instantly: the total is 40 hours and 0 minutes. In this case it works out cleanly, but most real-world totals do not.

Example with messy numbers:

  • Segment 1: 1:47:23
  • Segment 2: 0:55:41
  • Segment 3: 2:12:08
  • Segment 4: 0:38:52

Total: 5:34:04. Getting this right manually requires three separate carry-over calculations. A time calculator eliminates the errors.

Converting Between Time Formats

Different contexts require time expressed in different formats. This calculator converts between all common time representations.

Hours:Minutes:Seconds (HH:MM:SS). The standard format for displaying time durations. This is what you see on stopwatches, timers, and video players. 2:30:00 means 2 hours and 30 minutes.

Decimal Hours. Employers and payroll systems often require time expressed as a decimal. In this format, 30 minutes is 0.5 hours, 15 minutes is 0.25 hours, and 45 minutes is 0.75 hours. To convert minutes to decimal hours, divide by 60. So 2 hours and 20 minutes is 2.333 decimal hours (20/60 = 0.333).

Total Minutes. Some calculations are easier when everything is expressed in minutes. 2 hours and 30 minutes is 150 minutes. 1 day is 1,440 minutes. To convert HH:MM to total minutes, multiply hours by 60 and add minutes.

Total Seconds. Useful for precise timing in sports, science, and computing. 1 minute is 60 seconds, 1 hour is 3,600 seconds, and 1 day is 86,400 seconds.

Common Decimal Time Conversions

For quick reference when filling out timesheets, here are common minute values and their decimal hour equivalents.

  • 5 minutes = 0.08 hours
  • 10 minutes = 0.17 hours
  • 15 minutes = 0.25 hours
  • 20 minutes = 0.33 hours
  • 25 minutes = 0.42 hours
  • 30 minutes = 0.50 hours
  • 35 minutes = 0.58 hours
  • 40 minutes = 0.67 hours
  • 45 minutes = 0.75 hours
  • 50 minutes = 0.83 hours
  • 55 minutes = 0.92 hours
  • 60 minutes = 1.00 hours

To convert any number of minutes to decimal hours, divide by 60 and round to two decimal places. For payroll purposes, some companies round to the nearest quarter hour (0.25) or the nearest tenth of an hour (0.1 = 6 minutes).

Time Differences and Durations

Calculating the duration between two clock times requires attention to AM/PM and midnight crossings.

Same-day calculation. If a meeting starts at 9:30 AM and ends at 11:15 AM, the duration is simply 11:15 – 9:30 = 1 hour and 45 minutes.

Crossing noon. A shift from 10:00 AM to 3:30 PM spans 5 hours and 30 minutes. Convert to 24-hour format for easier math: 15:30 – 10:00 = 5:30.

Crossing midnight. A night shift from 10:00 PM to 6:30 AM crosses midnight. Add 24 hours to the end time: 30:30 – 22:00 = 8:30. The shift is 8 hours and 30 minutes.

Subtracting lunch breaks. If you work from 8:00 AM to 5:00 PM with a 1-hour lunch break, your worked time is 9 hours minus 1 hour = 8 hours. If the lunch break is 45 minutes, your worked time is 8 hours and 15 minutes.

For more detailed work-hour calculations with break deductions and overtime tracking, use the Hours Calculator.

Time Unit Conversions

For reference, here are the exact relationships between time units.

Seconds, minutes, and hours:

  • 1 minute = 60 seconds
  • 1 hour = 60 minutes = 3,600 seconds
  • 1 day = 24 hours = 1,440 minutes = 86,400 seconds

Days, weeks, months, and years:

  • 1 week = 7 days
  • 1 year = 365 days (common) or 366 days (leap)
  • 1 year = approximately 52.177 weeks
  • 1 year = 12 months (but months vary from 28 to 31 days)
  • Average month = approximately 30.437 days

Larger time units:

  • 1 decade = 10 years
  • 1 century = 100 years
  • 1 millennium = 1,000 years

Military Time (24-Hour Clock)

The 24-hour clock, often called "military time" in the United States, counts hours from 00:00 (midnight) to 23:59 (one minute before midnight). It avoids the AM/PM ambiguity that causes scheduling errors.

Conversion rules:

  • 12:00 AM (midnight) = 00:00
  • 1:00 AM to 11:59 AM = 01:00 to 11:59 (same numbers)
  • 12:00 PM (noon) = 12:00
  • 1:00 PM = 13:00 (add 12 to PM hours)
  • 11:00 PM = 23:00
  • 11:59 PM = 23:59

Quick conversion: For PM times, add 12 to the hour. For 24-hour times above 12, subtract 12 to get the PM equivalent. 15:30 = 3:30 PM. 20:00 = 8:00 PM.

The 24-hour clock is standard in most countries, aviation, medicine, and the military. Using it eliminates the possibility of confusing 8:00 AM with 8:00 PM, which is a meaningful safety benefit in medical and transportation contexts.

Frequently Asked Questions

How do I add hours and minutes together?

Add hours to hours and minutes to minutes separately. If the minutes total exceeds 60, subtract 60 from minutes and add 1 to hours. For example, 2:45 + 1:30 = 3:75, which becomes 4:15 after carrying over. This calculator handles the carry-over automatically.

How do I convert minutes to decimal hours?

Divide the number of minutes by 60. For example, 45 minutes = 45/60 = 0.75 hours. 20 minutes = 20/60 = 0.33 hours. This decimal format is commonly used on timesheets and payroll systems.

How do I calculate time between two clock times?

Subtract the start time from the end time. Use 24-hour format to avoid AM/PM confusion. For example, 5:00 PM to 9:30 PM is 17:00 to 21:30, a difference of 4 hours and 30 minutes. For times crossing midnight, add 24 to the end time before subtracting.

What is military time?

Military time uses a 24-hour clock running from 00:00 (midnight) to 23:59. It eliminates AM/PM confusion. To convert PM times, add 12 to the hour. 3:00 PM = 15:00. 10:30 PM = 22:30. Standard in aviation, medicine, and most countries outside the US.

How many seconds are in an hour?

There are exactly 3,600 seconds in one hour (60 minutes x 60 seconds). One day has 86,400 seconds. One week has 604,800 seconds.

How do I calculate total work hours for a week?

Enter each day’s hours and minutes into the calculator and add them up. The tool handles the base-60 arithmetic, converting excess minutes to hours automatically. For timesheet purposes, the result can be displayed in decimal hours.

What is 0.75 hours in minutes?

0.75 hours equals 45 minutes. Multiply the decimal portion by 60 to convert to minutes. So 0.5 hours = 30 minutes, 0.25 hours = 15 minutes, and 0.1 hours = 6 minutes.

Time calculations based on standard 60-second, 60-minute, 24-hour conventions. Data accurate as of: March 2026