Retainer and milestone invoices

Retainers and milestones are how you get paid during a longer job instead of waiting until the end. They are ordinary invoices with clearer descriptions. The hard part is making each payment easy to match against the work, so the client’s accounts person does not stall it.

Retainer vs milestone vs deposit

People mix these up. Keep the labels straight on the document so nobody argues later about what was already paid.

• Deposit. Money before work starts, usually a percentage of a fixed fee. Covered in detail in how to invoice a deposit.
• Retainer. A recurring fee that holds your time, or a prepaid bucket of hours. You invoice it on a schedule, often monthly.
• Milestone. A payment tied to a finished stage of a project: design approved, build shipped, handover complete.

Same tool for all three. Different wording on the line items and in the notes.

Invoicing a monthly retainer

Agree the amount, what it covers, and when it renews before the first invoice. Then keep every retainer invoice boring and consistent.

• One line item with a plain description, for example “Monthly design retainer, September 2026”.
• Quantity 1 and the agreed rate, or the hours included if you bill that way.
• A note that says whether unused hours roll over, expire, or are not tracked.
• The same invoice numbering habit you use for everything else. See invoice numbering.

If the retainer is prepaid hours and you later bill overage, put the overage on its own invoice or its own line. Do not rewrite last month’s retainer PDF.

Invoicing project milestones

Each milestone should be something the client can look at and say yes, that happened. Vague stages like “phase 2” create arguments. Better: “Homepage and four inner templates approved” or “Staging site handed over for UAT”.

On the invoice itself:

• Name the milestone in the line description, not only in the email subject.
• State the share of the project fee if you agreed percentages (for example 30% on approval).
• Reference the proposal or contract date in the notes so finance can find the original quote.
• Put the due date as a real date. Do not rely on “due on milestone” alone.

Send the milestone invoice when the stage is actually done, not when you hope it will be done next week. Payment terms start from the invoice date. More on terms in payment terms explained.

A simple milestone schedule

Example for a $10,000 fixed project with three stages. Each row is its own invoice, with its own number.

On the final invoice, note that prior invoices 1001 and 1002 covered $7,000 so the remaining balance is $3,000. You do not need a running ledger on every PDF, but the last one should make the total obvious.

What to put in the notes

• What this payment covers, in one sentence.
• What it does not cover, if scope often creeps.
• How many retainer hours remain, if you track that.
• The PO number, if the client uses purchase orders.
• Bank details or payment link, every time.

Common mistakes

• One invoice for the whole project sent on day one, then endless “we already paid part of this” emails.
• Reusing the deposit invoice number when you bill the next stage.
• Calling a retainer a deposit on the PDF when the contract used different words.
• Billing a milestone before the deliverable exists. Accounts will wait for confirmation from the project owner.

This is practical process, not legal advice. Your contract still decides what is owed if a project stops early. For the PDF itself, the invoice generator and the consultant template are enough for most retainer and milestone bills.