Hours and Minutes Calculator

This adds several lengths of time together and gives you one total. It exists because adding times is the arithmetic people most reliably get wrong on a calculator, and the reason is that a calculator works in base ten while time works in base sixty. Type 7.30 plus 8.15 into a phone calculator and it returns 15.45, which looks like an answer and is not one: 7 hours 30 minutes plus 8 hours 15 minutes is 15 hours 45 minutes, and the two only agree by coincidence. Change it to 7 hours 40 minutes plus 8 hours 30 minutes and the calculator says 16.10 while the true answer is 16 hours 10 minutes, which as a decimal is 16.17. Every entry here is kept as hours and minutes, converted to minutes internally, summed, and converted back, so the carry at sixty happens properly. You get the total as hours and minutes, the same total as decimal hours for entering into a payroll system, and the value at an hourly rate. Six rows is enough for a working week with a spare, and any row left at zero is simply ignored.

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35:00
total hours and minutes
Decimal hours35.00
Total minutes2,100
Entries counted5
Average per entry7:00
Pay at this rate$875

Adding times on an ordinary calculator fails because minutes carry at sixty, not at a hundred. Rows left at zero are ignored.

How it works

Each entry is converted to minutes by multiplying its hours by 60 and adding its minutes. The minutes are summed, then converted back: the total divided by 60, rounded down, is the hours, and the remainder is the minutes. Decimal hours are the total minutes divided by 60, which is the figure a payroll system wants. The average is the total divided by the number of entries that were not left at zero. Pay is the decimal hours multiplied by the rate.

Worked example

Take the five default entries: 7:30, 8:15, 6:45, 8:00 and 4:30. In minutes those are 450, 495, 405, 480 and 270, which sum to 2,100 minutes. Dividing by 60 gives 35 with no remainder, so the total is 35 hours 0 minutes, or 35.00 decimal hours. At $25 an hour that is $875. Note what an ordinary calculator would have done: 7.30 + 8.15 + 6.45 + 8.00 + 4.30 is 34.20, which is neither the right total nor a meaningful number.

Related calculators

Data sources: Employers in New Zealand must keep accurate records of hours worked under the Employment Relations Act 2000. See Employment New Zealand.

Frequently asked questions

Why can I not just add times on a normal calculator?

Because minutes carry at sixty and a calculator carries at a hundred. Adding 7.30 and 8.15 gives 15.45, which happens to look right, but 7.40 plus 8.30 gives 16.10 when the true answer is 16 hours 10 minutes, or 16.17 in decimal. The two only agree when the minutes happen not to carry.

How do I add hours and minutes together?

Convert everything to minutes, add them, then divide by 60. The whole number is the hours and the remainder is the minutes. For example 450 plus 495 minutes is 945, which is 15 hours and 45 minutes.

What is the decimal total for?

Payroll and invoicing systems usually want decimal hours rather than hours and minutes, so a total of 35 hours 30 minutes is entered as 35.5. The decimal figure here is the one to type into a payroll field.