Timesheet Invoices: How to Attach Proof of Work to an Invoice

Your client's accounts team has sent your invoice back with a one-line note: "Please attach a timesheet." Or an agency will not release payment until a manager has signed off your hours. Either way, the invoice on its own is not enough. They want to see the time behind the total.

This guide covers how a timesheet and an invoice work together, what approvers actually check, three ways to show proof of work, how to build a simple timesheet in a spreadsheet, and the mistakes that get invoices queried. If you are still working out how to price and lay out hourly lines, start with how to invoice for hours worked and come back here for the proof.

Timesheet vs invoice: what is the difference?#

They are two documents doing two jobs. The timesheet records the work. The invoice asks to be paid for it.

The invoice summarises and the timesheet itemises. A good timesheet invoice keeps the two in step, so every total on the invoice traces back to lines on the timesheet.

Dates matter on the invoice too, not only on the timesheet. UK government guidance lists "a clear description of what you're charging for" and the date the service was provided among the things an invoice must include. For time-based work, that means the billing period or the dates you worked belong on the invoice itself.

What do clients and agencies check before approving?#

Whoever approves your invoice is comparing three things: what was agreed, what the timesheet says, and what the invoice charges. They look for:

• The billing period. Do the dates on the timesheet match the period on the invoice, with no days from last month slipping in?
• The quantity. Does the total on the timesheet match the hours or days on the invoice exactly?
• The rate. Is it the rate in the contract or purchase order? Is any overtime or weekend rate one they agreed to?
• Approval. Has the right person signed off the time? Agencies often will not pay without it.
• Task descriptions. Can they tell what each block of time was for, in plain words?
• Their reference. Many larger clients need a purchase order (PO) number or project code to route the invoice to the right budget.

A mismatch on any of these usually means a query, and a query often sends the invoice back to the start of the approval queue. The fix is to make the checks easy before you send.

Three ways to show proof of work on an invoice#

You do not always need a separate timesheet. Pick the format that matches what your client asked for.

For day-rate work, a list of dates or a calendar is usually all a client needs: they want to see which days they are paying for. Day rate invoices covers that format in detail. For hourly work, approvers usually expect hours per day and a short task note, which means a timesheet.

How to make a simple timesheet in Google Sheets or Excel#

A timesheet does not need special software. A spreadsheet with seven columns covers almost every client.

1. Set up the columns

2. Add the hours formula

In E2, enter =(C2-B2)*24-D2/60 and format the cell as a number with two decimal places. Spreadsheets store times as fractions of a day, so multiplying by 24 turns the difference into hours. A 09:00 start, a 13:30 finish and a 30-minute break gives 4.00.

Fill the formula down the column, then total the billable hours at the bottom with =SUMIF(G2:G40,"Yes",E2:E40). If you only record durations, type them as decimals: 1 hour 20 minutes is 1.33, not 1.20.

3. Add a header and a sign-off block

At the top, put your name, the client's name, the billing period and the matching invoice number. At the bottom, add the total hours, the rate and the total amount, then two lines: "Approved by" and "Date". That block is what turns a list of hours into an approved record.

4. Export it and name it after the invoice

Save it as a PDF so nothing shifts when the client opens it, and give it the invoice number: INV-202610-004-timesheet.pdf. When accounts payable sees the two files side by side, they know they belong together.

How to get a timesheet approved without chasing#

Approval is where timesheet invoices usually stall, so make it the easiest step.

• Agree the routine at the start. Who approves your time, how (a signature, an email reply or the client's own portal) and by what day each month.
• Send the timesheet before the invoice. On the last working day of the period, send the timesheet and ask for a reply. Once you have "Approved", issue the invoice. It then goes through without a second round of checks.
• Keep the approval. An email that says "Approved, thanks" is a perfectly good record. Save it with the invoice.
• Flag overruns early. If a task ran long, say so in the task column and in your email before the client sees the total, not after.

Some agencies work the other way round. Under a self-billing arrangement, the client or agency prepares the invoice from your approved timesheet and sends you a copy with the payment. HMRC's VAT guidance on self-billing says a written agreement must be in place before it starts, and that while it runs you must not raise your own sales invoices for those transactions. If your agency self-bills, your job is to get the timesheet approved on time and check their figures.

A sample timesheet invoice#

Here is two weeks of hourly design work at £55 an hour, with the timesheet that goes with it. The names and figures are illustrative.

INVOICE                                    INV-202610-004
From:       Sam Ortiz Design, 12 Park Lane, Leeds
Billed to:  Northwind Studio Ltd, 4 Dock Street, Hull
Issue date: 15 Oct 2026          Due date: 29 Oct 2026
Period:     5 to 14 Oct 2026

Description                           Hours     Rate      Amount
Website design (timesheet attached)   38.50   £55.00   £2,117.50
-----------------------------------------------------------------
Total due                                              £2,117.50

Timesheet: INV-202610-004-timesheet.pdf
Hours approved by J. Patel by email, 14 Oct 2026

TIMESHEET: Sam Ortiz Design for Northwind Studio Ltd
Period 5 to 14 Oct 2026, invoice INV-202610-004

Date      Hours   Task
5 Oct      4.00   Homepage layout, round 2
6 Oct      6.50   Homepage layout, round 2
7 Oct      5.00   Product page templates
8 Oct      7.50   Product page templates
9 Oct      2.00   Client call and revisions
12 Oct     6.00   Checkout flow screens
13 Oct     4.50   Checkout flow screens
14 Oct     3.00   Final file prep and handover
Total     38.50   x £55.00 = £2,117.50

Approved by: J. Patel         Date: 14 Oct 2026

Notice that the invoice has one line and the timesheet carries the detail. The hours match to the quarter hour, and the approval is mentioned on the invoice so accounts payable does not have to ask.

Adding a work log to your invoice with BillBee.work#

For day-rate and monthly work, BillBee.work, a free invoice maker for freelancers, puts the proof on the invoice itself. Turn on Work log in invoice and it prints a small calendar of the days you billed, in every template, so the client sees exactly which days they are paying for without opening a second file.

The days come from the work you have already recorded:

• Pick the days on the small calendar for each service as you build the invoice, or
• Mark them through the month on the service calendar, where each service has its own colour, then choose Auto-fill from a logged month when you create the invoice. The services and their days fill in for you.

Then share the invoice by link. Your client opens it in a browser without an account, and on Pro they can also download a PDF. If you bill one client at the end of each month for the days you worked, monthly service invoices walks through that routine.

Be clear about what the work log is not. It shows days, not hours, start and end times, or task notes. If a client or agency needs hour-by-hour detail or a signed sheet, keep the spreadsheet above and send the PDF in the same email as the invoice link. BillBee.work does not send emails, so you paste the link into your own message anyway.

The same goes for hourly lines. BillBee.work counts 8 hours for each logged day on an hourly line, with no custom hours per day. For variable hours, bill the total as a fixed-amount line, such as "Website design, 38.5 h at £55", and let the timesheet carry the detail.

Mistakes that get timesheet invoices queried#

On that last point: BillBee.work has no PO number field. If a client needs one, add it to the service name, for example "Website design, PO 4471", so it prints on the line.

How long should you keep timesheets?#

Keep each timesheet, and the approval email, with your copy of the invoice. Together they back up the income you report.

How long depends on where you are taxed. HMRC says self-employed people must keep records for at least 5 years after the 31 January submission deadline of the relevant tax year. The IRS says to keep records that support income on a return until the period of limitations for that return runs out, which is 3 years in the standard case and longer in some situations. Elsewhere, check your tax authority's rules.

A simple habit makes this painless: one folder per client per year, with each invoice and its timesheet saved under the same number. For the rest of the billing process, from your first invoice to getting paid, see how to invoice as a freelancer.

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