Minutes to Decimal Hours: Why 8.30 Is Not 8:30

The conversion in one line

Decimal hours = whole hours + (minutes ÷ 60).

• 7:45 → 45 ÷ 60 = 0.75 → 7.75 hours
• 8:06 → 6 ÷ 60 = 0.10 → 8.10 hours
• 7:40 → 40 ÷ 60 = 0.666… → 7.67 hours
• 0:01 → 1 ÷ 60 = 0.0166… → 0.02 hours

Going the other way, multiply the decimal part by 60 to get minutes:

• 7.3 hours → 0.3 × 60 = 18 → 7:18
• 0.75 hours → 0:45
• 0.20 hours → 0:12
• 0.33 hours → 19.8 minutes, which rounds to 0:20. Two decimal places cannot hold 20 minutes exactly, so 0.33 is close, not equal.

Round half up to two places, once, at the end. 7:40 is 7.666… hours; the third digit is 6, so it rounds up to 7.67.

Minutes to decimal hours, 1 to 60

Find the minutes on the left of each pair and read the decimal on the right. The values for multiples of 3 minutes (3, 6, 9 … 60) come out exact; every other value is rounded to two places.

Three anchors are worth memorizing: 15 minutes is 0.25, 30 minutes is 0.50 and 45 minutes is 0.75. Six minutes is exactly one tenth of an hour, 0.10.

Why 8.30 is not 8:30, priced out

The mix-up runs both ways, and both cost real money. These examples use a $24.50 hourly rate, and each pay figure is worked from whole minutes.

An 8:30 shift entered as 8.30 hours. 8:30 is 8.50 hours. 8.30 hours is only 8:18. Paid as 8.30, the shift comes to $203.35 instead of $208.25: $4.90 short for one day, 12 minutes of work unpaid.

A weekly total copied without converting. Take a week whose time card adds up to 48:58. Converted correctly, that is 48.97 hours, and with 40 straight hours and the rest at time and a half the gross is $1,309.53. If someone types 48.58 instead, payroll is working from 48:35, which is 23 minutes short. Figured on those minutes, the gross falls to $1,295.44, which is $14.09 less. All 23 missing minutes come out of overtime: 8:35 of overtime instead of 8:58.

A day entered as 7.40 for 7:40. 7.40 hours is 7:24, so 16 minutes disappear. The guide to calculating hours worked prices this out on a full week.

The error can also run in the worker’s favor, as when 8.50 decimal hours (8:30) are read as 8:50 clock time and paid as 8.83 hours. Either way, the fix is the same: label every number as clock time (h:mm) or decimal hours, and never paste one into a field meant for the other.

Add in minutes, convert once

Rounding happens once, at the end. If you round each piece first, the rounding errors add up.

Here is the simplest case. Three separate pieces of 20 minutes each make exactly 1:00, which is 1.00 hour. Each 20 minutes on its own is 0.33 hours when rounded. Add three of those and you get 0.99, one hundredth short of the real total.

On one shift that is nothing. Over a year of daily totals, or across a whole crew, it is not. That is why a correct time card adds the days in hours and minutes, totals the week, and only then divides by 60. A week of 8:06, 10:15, 7:40, 10:30, 7:57 and 4:30 is 48:58, which converts to 48.97 hours.

Payroll records follow the same logic. Under 29 CFR 516.2, an employer must record the hours worked each workday and the total hours worked each workweek. The federal rule does not say whether those hours are kept as h:mm or decimals; Fact Sheet #21 says the law requires no particular form, only that the records be complete and accurate.

Tenths and quarter hours: rounding the punches is a different thing

Converting 7:40 to 7.67 does not change your time; it only writes it differently. Rounding the punches does change it. Some employers record punch times to the nearest 6 minutes (a tenth of an hour, so every day ends in .0 through .9) or the nearest 15 minutes (so every day ends in .00, .25, .50 or .75).

Under 29 CFR 785.48(b), rounding punches to the nearest 5 minutes, tenth of an hour or quarter hour is accepted for enforcement only if, over time, it does not fail to pay employees for all the time they actually worked. For quarter hours, the Department of Labor’s Fact Sheet #53 gives the split: 1 to 7 minutes may round down, and 8 to 14 minutes must round up. The same fact sheet warns that always rounding down may violate the law’s minimum wage and overtime rules.

So if your card shows 7.67 for a 7:40 day, nothing was rounded away. If it shows 7.50, the punches were rounded to the quarter hour, and the question becomes whether that rounding evens out over time. The guide to the 7-minute rule covers how to check.

Next step

Convert a single time, or print the full chart, with the time to decimal calculator. To total a whole week in minutes first and convert once, use the time card calculator. For the full procedure behind each day’s number, see how to calculate hours worked.