Time Calculator

A time calculator adds and subtracts hours, minutes and seconds by regrouping at 60 instead of 10. For example, 1 h 45 min 50 s + 2 h 30 min 25 s = 4 h 16 min 15 s, because 75 seconds is 1 minute 15 seconds and 76 minutes is 1 hour 16 minutes. For decimal hours, divide minutes by 60: 7 h 45 min = 7.75 hours.

How to use the time calculator

1. Pick a tab: Add / subtract for durations, Time between for hours worked between two clock times, Timecard for a week of shifts with overtime and pay, Add to a clock to find what time it will be, or Decimal hours to convert.
2. Choose the 12-hour (AM/PM) or 24-hour clock at the top. Times you have already typed are rewritten for you.
3. Type your numbers. Empty boxes count as 0, and decimals such as 1.5 hours are fine. In the first tab, use + Add another time for up to 10 rows and the + or − menu to subtract a row.
4. Read the answer in the green box, then open Show steps to see every carry and borrow worked out with your own numbers.

How to add and subtract time

Time is written in mixed units: days, hours, minutes and seconds. The rules that link them are fixed:

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

To add times, line them up in columns and add one column at a time, starting with the seconds. When a column reaches 60 seconds or 60 minutes, regroup it: keep the remainder and carry 1 to the next column. Hours carry into days at 24.

To subtract, work from the right again. If the top number in a column is smaller, borrow 1 from the next column. Borrowing 1 minute gives you 60 seconds, and borrowing 1 hour gives you 60 minutes. It works like ordinary borrowing, but with 60 instead of 10.

Hours between two times

To find the time between a start and an end time, first write both on the 24-hour clock. A PM time from 1:00 to 11:59 gets 12 added to the hour, 12:xx AM becomes 0:xx, and 12:xx PM stays 12:xx. Then subtract:

Time between = End time − Start time

If the end time is earlier than the start time, the period runs past midnight. Add 24 hours to the end time before subtracting. Subtract any unpaid break last.

Weekly timecard hours and overtime

For a week of shifts, work out each day as end time − start time − unpaid break, then add the days. Under the federal Fair Labor Standards Act, employees who are not exempt get overtime pay of at least 1.5 times their regular rate for hours over 40 in a workweek.

Say Monday to Friday add up to 37 h 45 min and a Saturday shift adds 4 h 30 min. The week is 42 h 15 min, or 42.25 hours: 40 regular hours and 2.25 overtime hours. At $18.50 an hour, pay is 40 × 18.50 + 2.25 × 18.50 × 1.5 = 740 + 62.4375 ≈ $802.44.

Employers may round clock times to the nearest 5, 6 or 15 minutes only if, over time, it does not cut pay for time worked.

Decimal hours formula

Timesheets and payroll often use decimal hours, where 7.5 means seven and a half hours. To convert:

• Decimal hours = hours + minutes ÷ 60 + seconds ÷ 3,600
• Minutes = decimal part × 60, and any decimal left in the minutes × 60 gives the seconds.

So 7 h 45 min = 7 + 45 ÷ 60 = 7.75 hours, and 7.33 hours = 7 h + 0.33 × 60 min = 7 h 19.8 min = 7 h 19 min 48 s.

Worked time calculation examples

Example 1: Adding up a week of shifts

You worked 7 h 45 min, 8 h 30 min and 6 h 50 min. Add the minutes first: 45 + 30 + 50 = 125 min. Since 125 min = 2 h 5 min, keep 5 min and carry 2 h. Add the hours: 7 + 8 + 6 + 2 = 23 h. The total is 23 h 5 min, which is 23 + 5 ÷ 60 ≈ 23.08 hours.

Example 2: An overnight shift with a break

A shift runs from 10:40 PM to 6:15 AM with a 45-minute unpaid meal break. On the 24-hour clock that is 22:40 to 06:15. The end is earlier than the start, so add 24 hours: 06:15 becomes 30:15.

Subtract the minutes: 15 is less than 40, so borrow 1 hour. That gives 75 − 40 = 35 min, and the hours become 29 − 22 = 7 h. The shift lasts 7 h 35 min. Take off the break: 35 min is less than 45 min, so borrow again: 95 − 45 = 50 min and 6 h remain. Time worked is 6 h 50 min ≈ 6.83 hours. At $20 an hour, the pay is about $136.67.

Example 3: What time will it be?

A bus leaves at 9:30 PM and the trip takes 8 h 45 min. On the 24-hour clock the start is 21:30. Add the minutes: 30 + 45 = 75 min = 1 h 15 min, so carry 1 hour. Add the hours: 21 + 8 + 1 = 30. A day has only 24 hours, so 30 − 24 = 6, and the date moves forward one day. The bus arrives at 6:15 AM the next day.

Example 4: Subtracting race times

One runner finishes in 3:05:20 and another in 2:48:45. Seconds: 20 is less than 45, so borrow 1 minute: 80 − 45 = 35 s. Minutes: the 5 became 4 after lending, and 4 is less than 48, so borrow 1 hour: 64 − 48 = 16 min. Hours: 2 − 2 = 0. The gap is 16 min 35 s.

Minutes to decimal hours chart

Every 6 minutes is exactly 0.1 hour, which makes a handy mental check.

Common mistakes with time math

• Reading decimals as minutes. 7.75 hours is 7 h 45 min, not 7 h 75 min, and 1.5 hours is 1 h 30 min, not 1 h 50 min.
• Carrying at 100. On a calculator, 1.45 + 2.30 gives 3.75, but 1 h 45 min + 2 h 30 min is 4 h 15 min.
• Forgetting the midnight crossing. From 10:00 PM to 6:00 AM is 8 hours, not −16 hours.
• Mixing up 12 AM and 12 PM. 12:00 AM is midnight at the start of the day and 12:00 PM is noon. The National Institute of Standards and Technology suggests writing “12 noon” or “12 midnight”, or using the 24-hour clock, to avoid confusion.
• Taking off paid breaks. Under US federal rules, short breaks of about 5 to 20 minutes count as hours worked. Usually only a real meal break of 30 minutes or more is unpaid, so subtract only that.

Where time calculations come up

People use these steps to check a paycheck, total study or practice time, plan a trip that arrives after midnight, compare race splits, and work out how long a playlist runs. Results here are arithmetic estimates; your employer’s payroll rules decide how time is rounded and paid.

Sources

• National Institute of Standards and Technology: Times of day (12 a.m., 12 p.m., noon and midnight)
• U.S. Department of Labor: Breaks and meal periods
• U.S. Department of Labor, Wage and Hour Division: Overtime pay
• 29 CFR 785.48: Use of time clocks (rounding of starting and stopping times)

Time practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

How do you add hours and minutes together?

Add the minutes and the hours separately. If the minutes come to 60 or more, subtract 60 from them and add 1 to the hours. For example, 2 h 40 min + 1 h 35 min: the minutes give 75 = 1 h 15 min, so the total is 2 + 1 + 1 = 4 h 15 min.

How do I calculate hours worked between two times?

Write both times on the 24-hour clock, subtract the start from the end, then take off any unpaid break. From 8:30 AM to 5:00 PM is 17:00 − 8:30 = 8 h 30 min; with a 30-minute lunch, that is 8 hours worked.

How do you calculate time that goes past midnight?

Add 24 hours to the end time, then subtract as usual. From 11:30 PM to 2:15 AM: 2:15 becomes 26:15, and 26:15 − 23:30 = 2 h 45 min.

What is 7.75 hours in hours and minutes?

The whole number is the hours and the decimal part times 60 is the minutes: 0.75 × 60 = 45. So 7.75 hours is 7 hours 45 minutes. Going the other way, divide the minutes by 60: 45 ÷ 60 = 0.75.

Is 12 AM midnight or noon?

12:00 AM is midnight, the start of a new day, and 12:00 PM is noon. On the 24-hour clock they are 00:00 and 12:00. Because the labels confuse many people, NIST recommends writing "12 noon" and "12 midnight" instead.

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