Flat Fee Invoice: When and How to Use It
A flat fee invoice bills one agreed price instead of hours. When to use it, what to include, a filled example with deposit math, and wording to avoid disputes.
A flat fee invoice charges one agreed price for a defined job, such as $1,500 for a logo package or £350 for a tax return, instead of billing hours or materials. Use it when you can describe the scope clearly in advance and estimate your effort with confidence. The invoice itself is simple: a clear description of what the fee covers, any deposit already paid, and the balance due.
This guide explains when flat-fee billing works well, what to put on the invoice, how to handle deposits and scope changes, and gives a complete worked example.
Flat fee vs hourly billing
With hourly billing, the client pays for your time and carries the risk if the job takes longer. With a flat fee, the price is fixed and you carry that risk, but you also benefit if you work efficiently. Our comparison of fixed price vs time and materials contracts covers the trade-offs in depth. In short:
| Flat fee | Hourly | |
|---|---|---|
| Price known in advance | Yes | Estimate only |
| Who carries overrun risk | You | Client |
| Timesheets needed | No | Yes |
| Best for | Repeatable, well-defined work | Open-ended or uncertain work |
| Invoice detail | Deliverables | Hours, dates, tasks |
When to use a flat fee invoice
- Packaged services: a website audit, a 10-image product shoot, a will, a bookkeeping clean-up.
- Repeat work you know well, where you can predict the effort within a narrow range.
- Clients who need budget certainty, such as small businesses or grant-funded organisations.
- Work where hours undersell value, for example when your experience lets you finish quickly.
Avoid flat fees when the scope is vague, depends heavily on the client's input, or involves unknowns like old code or hidden building defects. If you are still working out the number itself, our guide on how to price your services walks through cost-plus and value-based approaches.
What to include on a flat fee invoice
- Your business details and tax ID, and the client's legal name and address
- A unique invoice number, the invoice date and the due date
- The date the work was delivered (the supply date), required on invoices in the UK and many other countries, as the UK government's invoice checklist notes
- A scope description listing the deliverables the fee covers
- A reference to the quote, proposal or contract that set the price
- Any deposit or milestone payments already received
- Separate lines for approved extras
- Tax, if you are registered, and the total
- Payment terms and how to pay
The description does most of the work on a flat fee invoice. Instead of "Design services", write "Brand identity package per Quote Q-118: primary logo, two variations, colour palette, one-page style sheet, two revision rounds". Our guide to writing invoice line item descriptions has more examples.
Flat fee invoice example
A designer quoted a flat $2,400 for a brand identity package, with 50 percent upfront. During the project the client approved one extra item. Here is the final invoice.
| Description | Qty | Price | Amount |
|---|---|---|---|
| Brand identity package, flat fee per Quote Q-118 (logo, 2 variations, palette, style sheet, 2 revision rounds) | 1 | $2,400.00 | $2,400.00 |
| Additional item: social media profile kit (approved by email 4 Nov 2026) | 1 | $300.00 | $300.00 |
| Subtotal | $2,700.00 | ||
| Less: deposit received 2 Oct 2026 (Invoice D-0031) | -$1,200.00 | ||
| Balance due by 27 November 2026 | $1,500.00 | ||
The math: the 50 percent deposit was $2,400 x 0.5 = $1,200. The final total is $2,400 + $300 = $2,700, minus $1,200 already paid, leaving $1,500. Showing the deposit line with its own invoice reference stops the client paying the full amount twice or querying the balance. For the deposit invoice itself, see our guide to billing an advance payment.
How to write a flat fee invoice, step by step
- Start from the accepted quote. Copy the agreed price and scope wording exactly.
- Add the invoice basics: number, dates, both parties' details.
- Write the flat fee as one line with the scope in the description. Quantity 1, price equals the fee.
- Add approved extras as separate lines, each with the approval reference.
- Deduct payments already received, quoting the earlier invoice numbers.
- Apply tax to the right amount if you are registered, then check the total.
- State the terms and send it promptly once the work is delivered.
Splitting a flat fee into stages
On larger jobs, a single invoice at the end leaves you exposed for weeks. A common structure is a deposit on signing, a payment at a midpoint deliverable, and the balance on completion. Each stage is a separate invoice, and each one should show the full fee, what has been billed so far, and what remains. Our explainer on how milestone payments work shows how to set those stages. For multi-phase work, a project invoice template with stage billing can be easier to manage.
Flat fee invoice examples by industry
The structure stays the same across professions, but the description changes. A few examples of clear flat-fee lines:
| Industry | Example line | Fee |
|---|---|---|
| Accounting | Sole trader self-assessment return, tax year 2025-26, including one meeting | £350 |
| Photography | Product photography package: 15 edited images, white background, web and print sizes | $900 |
| Web design | Five-page brochure website per Proposal P-22, including contact form and basic SEO setup | $3,200 |
| Legal | Drafting of shareholder agreement for two founders, one revision round | £1,200 |
| Trades | Supply and fit kitchen tap, remove old tap, test for leaks (parts included) | $240 |
Each one names the deliverable, sets its limits, and points back to the quote or proposal where possible. That is what lets a client approve the invoice without asking questions.
Tax on a flat fee
A flat fee is taxed like any other charge. If you are registered for VAT, GST or sales tax and the service is taxable, add tax to the fee unless your quote clearly said the price included tax. Agree this in advance: "$2,400 plus applicable tax" and "$2,400 including tax" lead to different totals. For a $2,400 fee and a 10 percent tax rate, the first gives a total of $2,640, while the second means the fee is really $2,181.82 plus $218.18 tax. State on the quote and the invoice which one applies.
Checking that a flat fee still pays
Because you carry the overrun risk, track your actual time on flat-fee jobs privately, even though it does not go on the invoice. If a $2,400 package regularly takes 40 hours, your effective rate is $60 an hour. If it creeps up to 55 hours, the effective rate drops to about $44. Reviewing this every few jobs tells you when to raise the price or tighten the scope.
Flat fee invoice checklist
Before you send a flat fee invoice, run through these questions:
- Does the fee match the accepted quote or contract exactly?
- Does the description name the deliverables, not just the type of service?
- Is the quote, proposal or contract number referenced?
- Have all approved extras been added, each with its approval reference?
- Have deposits and earlier stage payments been deducted, with their invoice numbers?
- Is tax applied in the way the quote said it would be (added on top, or included)?
- Is the due date shown as an actual calendar date?
- Are payment details complete, including the reference the client should use?
If all eight are covered, the client's approver has everything needed to sign off the invoice in one look.
Wording that prevents flat fee disputes
Most flat fee disputes come from scope rather than price. The client remembers agreeing to "the website" and you remember agreeing to five pages. Clear wording on the quote, repeated on the invoice, settles this before it starts.
- State what is included and, just as importantly, what is not: "Copywriting not included."
- Limit revisions: "Includes two rounds of revisions; further rounds billed at $80 each."
- Set a validity window for the client's input so a job cannot stall for months.
- Explain change requests: "Work outside this scope will be quoted separately before it starts."
Common mistakes
- Vague descriptions like "Services rendered" that give the client nothing to approve against.
- Adding unapproved extras to the final invoice, which almost always causes a dispute.
- Forgetting to deduct the deposit, so the client sees a higher total than expected.
- Listing hours on a flat fee invoice, which turns the conversation back to your hourly rate.
A flat fee invoice takes a few minutes once the scope is written down. Our free invoice generator lets you add the fee, extras and deposit lines, then download a clean PDF, with no account needed.
Frequently asked questions
What is a flat fee invoice?
A flat fee invoice bills a single, pre-agreed price for a defined piece of work, rather than charging by the hour or by materials used. The client knows the cost in advance, and you keep any efficiency gains. The invoice still needs normal details such as a number, dates, both parties' details and payment terms, plus a clear description of the scope the fee covers.
Do I need to show hours on a flat fee invoice?
No. The point of a flat fee is that the price does not depend on time, so hours are not required and showing them can invite questions about your hourly rate. Describe the deliverables instead. If a client or funder asks for an hours breakdown for their own records, you can provide it separately, but keep the invoice itself focused on what was delivered.
Can I charge extra on a flat fee job?
Only for work outside the agreed scope, and ideally only after the client approves it in writing. Add a separate line for each change, such as "Additional landing page, approved by email 4 Nov", with its own price. Write a change clause into your quote or contract so both sides know how out-of-scope requests are priced before they come up.
Should a flat fee be paid upfront?
Many flat-fee providers take part of the fee upfront, often 25 to 50 percent, with the balance on completion. Small jobs are often billed in full on completion or in full upfront. For larger jobs, splitting the fee into milestones reduces your risk. Whatever you choose, show deposits already paid on the final invoice so the balance due is clear.
Is a flat fee the same as a fixed price?
In everyday use they mean much the same thing: one agreed price for a defined scope. "Flat fee" is common for services like legal work, design, tax returns or photography packages. "Fixed price" is more common in contracting and software, where it is contrasted with time and materials. Both rely on a clearly written scope to avoid disputes.
Invoice Creator Editorial Team
Guides on invoicing, cash flow and small-business finance from Invoice Creator, operated by Next Software Development Company. Content is reviewed for accuracy against the fields our own invoice generator produces.
Try the invoice generator