How to Calculate Hours Worked for a Timesheet (and Convert Minutes to Decimals)

Adding up hours sounds easy until you try to do it on a calculator. Time is counted in sixties, calculators count in tens, and the gap between the two is where most timesheet and invoice errors come from.

Step 1: work out each day

Subtract the start time from the finish time, then take off unpaid breaks.

Start 8:45, finish 17:15, 30-minute lunch:

8:45 to 17:15 is 8 hours 30 minutes.
Minus 30 minutes is 8 hours.

Do the subtraction in hours and minutes, not decimals. Typing 17.15 − 8.45 into a calculator gives 8.70, which is meaningless.

Step 2: overnight shifts

If a shift crosses midnight, split it at midnight. A shift from 22:00 to 06:30 is 2 hours before midnight and 6 hours 30 minutes after, so 8 hours 30 minutes in total. Alternatively, add 24 hours to the finish time (30:30 − 22:00 = 8:30).

Step 3: convert minutes to decimal hours

Payroll systems and invoices usually want decimal hours. Divide the minutes by 60:

6 minutes = 0.1 hours
15 minutes = 0.25 hours
20 minutes = 0.33 hours
30 minutes = 0.5 hours
40 minutes = 0.67 hours
45 minutes = 0.75 hours
50 minutes = 0.83 hours

So 7 hours 40 minutes is 7.67 hours, not 7.40.

That single mistake is expensive. At 40 an hour, billing a 7:30 day as 7.3 hours charges 292 instead of 300. Over a month of daily entries the gap adds up to a day's pay.

Step 4: add up the week

A week of 8:00, 7:45, 8:30, 6:15 and 7:40 converts to 8 + 7.75 + 8.5 + 6.25 + 7.67 = 38.17 hours, which is 38 hours 10 minutes.

Multiply decimal hours by the hourly rate to get pay: 38.17 × 18 = 687.06.

Rounding rules

Many employers round clock times to the nearest 5, 6 or 15 minutes. In the United States, a common approach under federal rules is the "7-minute rule" for 15-minute rounding: 1 to 7 minutes rounds down and 8 to 14 rounds up. Rounding is allowed only if it is neutral over time, so it cannot always favour the employer. Check your local rules and your contract.

Overtime

Overtime thresholds vary. In the US the federal threshold is over 40 hours in a workweek, paid at 1.5 times the regular rate. Some states also have daily overtime rules. In the UK there is no legal overtime premium, but average weekly hours are capped at 48 unless you opt out. Track daily totals as well as the weekly sum so you can apply whichever rule applies to you.

Keep a record

Write times down when they happen, not at the end of the week. Memory rounds generously in both directions, and a contemporaneous record is what settles a dispute about pay.

Let the calculator do it

The time difference calculator gives the gap between two times in hours and minutes and as decimal hours. For weekly, monthly and yearly totals with pay, use the work hours calculator, and the salary to hourly calculator converts an annual salary into an hourly rate.