Getting paid

Billing by the hour: timesheets, rounding and the invoice

How to invoice hourly work so clients trust the hours: keeping time, writing hours as decimals, fair rounding, what to attach, caps and estimates, and how the line on the invoice should read.

30 Oct 2026 · 7 min read

A week of time becomes one invoice line. Add the minutes, turn them into decimal hours, round once, then multiply by the rate.

Marco bills a client in Sydney A$140 an hour for analytics work. His first invoice says “Consulting, 7.45 hours”. The client reads it as seven and a half hours and wonders where the extra time came from. Marco meant 7 hours 45 minutes, which is 7.75 hours. Both numbers are wrong for different reasons, and the invoice waits while they sort it out. Hourly billing works when the client can see where the hours came from and the arithmetic is beyond doubt.

Agree the rules first

The rate, and whether it differs for some work, such as travel time, urgent work or weekends.
How time is rounded, in what step, and whether up or to the nearest.
A cap or estimate, and what happens when you near it.
How often you invoice: weekly, every two weeks, monthly, or at the end of the job.
What you send with the invoice: a summary, or every entry.

One email the client replies to is enough. It turns later questions into a reference.

Keep time as you go

Write down time the same day: the date, what you did in a few words, start and end or the duration. Time rebuilt from memory at the end of the month is always lower than what you worked, and harder to defend. Any timer app or a spreadsheet will do. What matters is that each entry has a date and a task the client would recognise.

Write hours as decimals

An invoice multiplies a quantity by a rate, so the quantity has to be a decimal number of hours. Divide the minutes by 60.

Time	Decimal hours
6 minutes	0.1
15 minutes	0.25
20 minutes	0.33
30 minutes	0.5
45 minutes	0.75
1 hour 50 minutes	1.83

So 7 hours 45 minutes is 7.75, never 7.45. If you write hours and minutes on the timesheet, convert only the total for the invoice.

Rounding time fairly

Most people round time to a step: 6 minutes (a tenth of an hour, common with lawyers and accountants), 15 minutes, or 30 minutes for short calls. Two questions decide whether it is fair.

Each entry, or the total? Rounding each entry up adds a little every time. Three entries of 2h 10m, 1h 50m and 3h 05m are 7h 05m in all. Rounded up to 15 minutes each, they become 2h 15m, 2h 00m and 3h 15m: 7.5 hours. Rounded once on the total, 7.25 hours.
Up, or to the nearest? Rounding up always favours you. Rounding to the nearest step evens out over a month.

Either can be fair if it was agreed and you apply it the same way every time. Say it on the invoice in a few words: “Time rounded up to the next 15 minutes.” What causes trouble is a minimum charge nobody mentioned, such as billing every two-minute email as a quarter hour.

What the invoice line says

One line per kind of work and rate, with the period. Quantity in hours, the hourly rate, the amount.

“Data and reporting consulting, 5 to 8 Oct: 7.25 hours at A$140”, A$1,015.00.
“Travel time, 2 trips to Parramatta: 3 hours at A$70”, A$210.00, if travel is billed at a lower rate.

Separate lines for separate rates. Lumping them together hides the rate and makes the total hard to check. Our guide to writing invoice line items has more examples.

Send the timesheet with it

A short timesheet, attached or pasted below the invoice email, answers the question before it is asked. Date, task, time, and the total that matches the invoice. For a client who does not want the detail, a summary is enough: “12 hours in October: 7 on the data model, 5 on the report”. Keep the full record either way, in case they ask later.

Caps and estimates

If you gave an estimate of 20 hours, tell the client when you reach 15, not after 28. “We are at 15 of the 20 hours. The report needs about 8 more. Shall I go on?” An hourly invoice that runs far past the estimate without warning is the one most often disputed. If the client agreed a hard cap, the invoice stops at the cap unless they approved more in writing.

Bill often

On long hourly jobs, invoice every two weeks or every month rather than at the end. The amounts stay small enough to approve quickly, the client sees the hours while they still remember the work, and you are not waiting months for money. See also retainers, when the client wants a fixed number of hours each month, and when to send an invoice.

In Openn InvoiceOpenn Invoice does not track time, so keep your timesheet where you like. On the invoice, pick Hour in the Unit list, type the hours as a decimal in Qty (7.25 works) and your hourly rate in Rate. Save each kind of work under Items with its unit and rate, so the next invoice takes a moment. Use the Note to customer box for a short summary of the hours or your rounding rule. Invoices cannot carry an attached file, so send the timesheet in the same email or message.

The short version

Agree the rate, the rounding step, any cap and how often you invoice, in writing.
Log time the same day, with a date and a task the client recognises.
Bill hours as decimals: 7 hours 45 minutes is 7.75.
Round the same way every time, and say how on the invoice.
Send a timesheet or summary with each invoice, and warn early when you near an estimate.