An hour and thirty minutes is 1.5 decimal hours, not 1.30. To convert hours and minutes to decimal hours, divide the minutes by 60 and add the whole hours.
That sounds too basic to cause a billing problem. Then someone exports a timesheet, pastes it into a spreadsheet, and treats the digits after the decimal point as minutes. The report still looks plausible. The invoice is wrong.
For an agency billing multiple people across multiple projects, a small format mistake can travel a long way before anyone notices.
The conversion formula
Decimal hours = whole hours + (minutes ÷ 60)
For two hours and 45 minutes:
2 + (45 ÷ 60) = 2.75 hours
If you have the entire duration in minutes, divide that number by 60. A 165-minute session is also 2.75 hours.
The reverse calculation is just as straightforward. Keep the whole hours and multiply the decimal fraction by 60. For 2.75 hours, the fraction is 0.75; multiplying it by 60 gives 45 minutes.
The decimal point is a fraction of an hour. The colon in a duration such as 2:45 separates hours from minutes. Those two formats can describe the same amount of work, but their digits are not interchangeable.
A quick timesheet conversion chart
The decimal values below are shown to four places where needed. Values marked approximately are rounded displays; retain the original duration for calculations.
| Minutes | Decimal hours | Example with two whole hours |
|---|---|---|
| 5 | ≈ 0.0833 | ≈ 2.0833 |
| 6 | 0.1000 | 2.1000 |
| 10 | ≈ 0.1667 | ≈ 2.1667 |
| 12 | 0.2000 | 2.2000 |
| 15 | 0.2500 | 2.2500 |
| 20 | ≈ 0.3333 | ≈ 2.3333 |
| 24 | 0.4000 | 2.4000 |
| 30 | 0.5000 | 2.5000 |
| 36 | 0.6000 | 2.6000 |
| 40 | ≈ 0.6667 | ≈ 2.6667 |
| 45 | 0.7500 | 2.7500 |
| 50 | ≈ 0.8333 | ≈ 2.8333 |
| 54 | 0.9000 | 2.9000 |
| 60 | 1.0000 | 3.0000 |
Six-minute increments convert neatly because six minutes is one tenth of an hour. That makes them convenient to display. It does not mean every agency should bill in six-minute increments.
What a format error does to an invoice
Suppose a designer records 2 hours and 30 minutes at an agreed rate of $120 per hour. This is an illustrative example, with no tax or expenses.
The correct calculation is:
2.5 × $120 = $300
If someone enters 2.30 as a decimal number instead:
2.3 × $120 = $276
The difference is $24 for one entry. A value of 2.30 decimal hours actually means two hours and 18 minutes.
The solution is to label the field. Use “Duration, hours:minutes” or “Duration, decimal hours” in the export and in the working spreadsheet. A column called “Time” leaves the reader to guess.
Conversion and rounding are different decisions
Conversion changes the representation. Rounding changes the precision or the billable quantity.
Twenty minutes equals one third of an hour. Displaying that as 0.33 is a rounded decimal display. Billing the same session as 30 minutes changes the quantity being charged.
Decide how billing increments work in your client agreement and apply them consistently. Keep the recorded duration available even when the billing calculation uses a different increment. That gives you an honest record for both client questions and internal profitability analysis.
There is also a smaller arithmetic trap: rounding every converted entry before adding the entries together.
Three separate 20-minute entries total exactly one hour. If each is reduced to 0.33 before summing, the result is 0.99. At $150 per hour, that produces $148.50 instead of $150.
Retain the source precision during calculation. Apply the agreed billing rule at the intended level—entry, task, day, or invoice—and round currency according to the invoice calculation method. Make that method consistent between the supporting report and the invoice.
Make the export reconcile before sending it
Start with a small check that includes a whole-hour entry, a half-hour entry, and an awkward duration such as 20 minutes. Compare the source timesheet, exported duration, and resulting amount.
Then check the complete report against the invoice using the same date range, approved entries, billable status, rates, and billing rules. An exact duration match can still produce a different amount if a rate changed during the period.
If the file contains spreadsheet time values rather than ordinary decimal numbers, confirm their underlying format before applying a rate. A cell that displays 2:30 may store a fraction of a day. Pasting or reformatting it does not necessarily convert it into decimal hours.
The operating rule is simple: preserve the original duration, make the export format explicit, and investigate a mismatch before adjusting a total by hand.
Common questions
Is 7.30 hours the same as seven hours and thirty minutes? No. As a decimal, 7.30 hours is seven hours and 18 minutes. Seven hours and thirty minutes is 7.5 hours.
What is 45 minutes in decimal hours? 0.75 hours. Divide 45 by 60.
Should I round every time entry to two decimal places? You can display two decimal places, but preserve the underlying duration for calculation. Early rounding can change the total.
What should I send the client? Use the format the client understands and the billing calculation requires. Explain the format once, then keep it consistent across reporting periods.
Time Trakkr supports reporting exports and invoicing from tracked time. Explore the reporting and invoicing workflow, then use the same approved records for both sides of the reconciliation.
Read next: From tracked hours to an invoice that gets paid and A timesheet approval process people don't resent.
