How to invoice for a fixed-price project

Set the payment schedule with the price

A fixed fee quoted without a payment schedule usually becomes one invoice at the end, which puts the whole amount at risk. Put the schedule in the quote: what is due on acceptance, what is due at each stage and what is due on completion.

A common shape for a mid-sized project is a deposit to start, one or two milestone payments and a balance on delivery. Match the milestones to things the client can see happening, not to your internal effort.

Invoice the deposit against a named trigger

The deposit invoice should say what it secures—booked dates, initial materials, discovery work—and state how it is applied later. Write the line as “Deposit, 30% of agreed project fee” rather than an unexplained amount, and start the project only once it clears.

Make each milestone invoice self-explanatory

A milestone invoice is easier to approve when it names the stage, restates the total project fee and shows how much of it this invoice represents. Someone in finance who never spoke to you should be able to read it without asking a question.

• Reference the quote or contract number on every invoice in the series.
• Show the stage: “Stage 2 of 3 — design sign-off”.
• State the cumulative position: invoiced to date and remaining.
• Keep the invoice numbers sequential with the rest of your books, not restarted per project.

Handle scope changes as their own line or invoice

Extra work should never be quietly folded into a milestone amount—that is what turns a final invoice into a dispute. Get the change approved in writing with its own price, then bill it either as a clearly labelled variation line or as a separate variation invoice referencing the approval.

If a change affects the schedule as well as the fee, say so at the point of approval rather than on the invoice.

A worked example

A website build is agreed at 6,000 in the client’s currency: 30% deposit, 40% at design sign-off, 30% on launch. The deposit invoice is 1,800; the second is 2,400 and names the signed-off designs; the final is 1,800 plus an approved variation line of 450 for an extra language version, so 2,250.

Each invoice shows the 6,000 project total and the amount invoiced to date, so the client can reconcile the series at a glance.

Close the project cleanly

The final invoice should confirm that it is final, list any variations, show the deposit and earlier payments deducted, and state the balance due with an actual date. Send it as soon as the completion trigger is met, and keep the quote, approvals and invoices together in one place.