Add and subtract time

How do I add hours and minutes?

Add the minutes and the hours separately, then carry every 60 minutes over as an hour. 2 h 45 min + 1 h 30 min: 45 + 30 = 75 minutes, which is 1 h 15 min; 2 + 1 + 1 = 4 hours. The total is 4 h 15 min.

How do I subtract time?

Borrow an hour when you need more minutes. 5 h 10 min − 2 h 40 min: borrow to get 4 h 70 min, then 70 − 40 = 30 minutes and 4 − 2 = 2 hours — 2 h 30 min. Switch any line to "Subtract" to take it away from the total.

How do I convert hours and minutes to decimal hours?

Divide the minutes by 60 and add them to the hours. 4 h 15 min is 4 + 15 ÷ 60 = 4.25 hours; 7 h 40 min is 7.67 hours. Payroll and time sheets often use decimal hours.

What time will it be in 3 hours and 30 minutes?

Switch to "Clock time" and add the duration to the start time. 9:45 AM + 3 h 30 min = 1:15 PM. If the answer passes midnight, the calculator says it is the next day.

How many minutes are in 2.5 hours?

Multiply by 60: 2.5 × 60 = 150 minutes, or 2 h 30 min. The table under the result shows any total in hours, minutes and seconds.

How do I find the time between two clock times?

Subtract the earlier from the later. From 8:40 AM to 1:15 PM, the difference is 4 h 35 min. If the end time is earlier on the clock than the start, the span crosses midnight and you add 24 hours first: from 10:30 PM to 6:15 AM is 7 h 45 min.

How many seconds are in a day?

86,400: 24 hours × 60 minutes × 60 seconds. A week is 604,800 seconds. The calculator treats every day as exactly 24 hours.

How the calculator works

Every entry is converted to seconds: hours × 3,600 plus minutes × 60 plus seconds. Added entries increase the total and subtracted entries decrease it, and the sum is turned back into hours, minutes and seconds. In clock mode the start time is converted to minutes after midnight, the duration is added or subtracted, and the answer is shown on a 12-hour clock with a note when the result falls on another day. The table below the result shows the total as hours, minutes and seconds. Because the arithmetic uses minutes and seconds, it never needs the "carry the 60" step by hand.

Worked example: adding two durations and a work week

Add 1 h 50 min 30 s and 2 h 25 min 45 s. The seconds are 30 + 45 = 75, so 15 seconds with 1 minute carried. The minutes are 50 + 25 + 1 = 76, so 16 minutes with 1 hour carried. The hours are 1 + 2 + 1 = 4. The total is 4 h 16 min 15 s. For a week with shifts of 7 h 50 min, 8 h 15 min, 6 h 40 min, 8 h 5 min and 7 h 30 min, the minutes add up to 2300, which is 38 h 20 min, or 38.33 decimal hours. A start at 10:30 PM plus 3 h 45 min ends at 2:15 AM on the next day.

Decimal hours and payroll

Time sheets often need decimal hours: divide the minutes by 60. 7 h 50 min is 7 + 50 ÷ 60 = 7.83 hours, not 7.50, and 8 h 15 min is 8.25. Multiplying decimal hours by an hourly rate then gives pay. Employers may round to the nearest quarter hour or tenth of an hour under their own policy, which this calculator does not apply.

Common mistakes

Treating minutes as decimals is the most frequent one: 2.30 hours is 2 h 18 min, not 2 h 30 min. Adding minutes without carrying over every 60 is the same error in a different form. On a 12-hour clock, 12:00 AM is midnight and 12:00 PM is noon, and mixing them up shifts a result by 12 hours. The calculator also counts every day as 24 hours, so a span that includes a daylight saving change differs from the wall-clock difference by an hour; for dates across a time change, use a date calculator or the time zone converter.

Sources: the second as the SI unit of time and the conversions 1 min = 60 s, 1 h = 3,600 s and 1 day = 86,400 s (NIST SP 811, Appendix B.8). Related: time card calculator, time zone converter and date calculator.