Retainer Invoices: How to Bill a Monthly Retainer (With a Sample)

A client wants to keep you on a monthly retainer: a fixed fee each month for a set amount of your time. It is steady income and less selling. Then the first invoice raises questions. Do you bill at the start of the month or the end? What if they use more time than the fee covers, or less?

This guide answers those, with a sample retainer invoice, a month-to-month routine you can run in Word or a spreadsheet, and the mistakes that cause friction. For the basics that apply to every invoice, see how to invoice as a freelancer.

What is a retainer invoice?#

A retainer invoice bills a regular, fixed fee for an ongoing arrangement, rather than for work already measured. The word "retainer" covers a few different deals, so be sure you and the client mean the same one.

Prepaid time and fixed scope are the two you will meet most often. Whichever yours is, write it down in an agreement before the first invoice.

Two neighbours often get confused with retainers. A deposit is part of one project's price paid upfront, then deducted from the final bill; deposit invoices covers those. And if you bill a client each month for however many days you actually worked, that is monthly billing, not a retainer: see monthly service invoices.

What should a retainer invoice include?#

On top of the usual details (your name, the client's, an invoice number, dates, payment details), a retainer invoice needs to answer the questions an accounts team will ask:

• The period covered. "1 to 30 November 2026", not just "November retainer".
• What the fee includes. "Up to 4 days", "up to 20 hours" or the list of deliverables.
• The fee itself, on its own line.
• Extra work, if any, on separate lines with dates, quantity and rate.
• Your unused time rule, in a few words, such as "Unused days expire at month end".
• A reference to the agreement, so the client can check the terms.
• A due date, usually before or on the first day of the period.

UK government guidance lists the date the service was provided among the things an invoice must include. For a retainer, the period covered does that job, so never leave it off.

Should you bill a retainer in advance or in arrears?#

The hybrid is common and easy to defend. In late October you invoice November's fee, plus any extra days worked in October, due at the start of November. You are paid before you start each month, and the client only pays for extra work once it has happened.

How to handle extra work and unused time#

These two questions are behind many retainer disputes. Settle both in the agreement and repeat them on the invoice.

Extra work. Agree an overage rate and a rule for approving it. Many freelancers price the retainer slightly below their usual day rate in return for the commitment, and charge extra days at the full rate. Ask for approval by email before you go over, then bill the extra days as their own lines with dates.

Unused time. Pick one of these:

Unlimited rollover sounds generous, but it can pile up into a month where the client is owed more days than you have. A short limit protects both sides.

A sample retainer invoice#

Here is a hybrid retainer for a content strategist: £2,000 a month for up to 4 days, extra days at £550, VAT registered. The names and figures are illustrative.

INVOICE                                       AM-202610-002
From:       Alex Morgan Content, 9 Quay Road, Bristol
Billed to:  Fernleaf Foods Ltd, 22 High Street, Bath
Issue date: 23 Oct 2026          Due date: 2 Nov 2026

Description                                Qty      Rate      Amount
Monthly retainer, 1 to 30 Nov 2026          1  £2,000.00   £2,000.00
  (up to 4 days; unused days expire)
Additional day, 21 Oct 2026                 1    £550.00     £550.00
  (approved by email, 19 Oct)
-------------------------------------------------------------------
Subtotal                                                  £2,550.00
VAT (20%)                                                   £510.00
Total due                                                 £3,060.00

Per retainer agreement dated 3 Sep 2026.

The fee and the extra day sit on separate lines, the period is explicit, and the extra day carries the date and the approval. Nothing here needs an email to explain it.

How to set up a monthly retainer invoice in Word or a spreadsheet#

1. Build a master copy

Make the invoice once with your details, the client's details, the retainer line, the agreement reference and your payment details. Save it as "Retainer master" and never send it.

2. Duplicate it each month

On the same day each month, copy the master, give it the next invoice number, and update the issue date, due date and period. Each month needs its own invoice with its own number. Resending last month's file with a new date causes problems in both sets of books.

3. Add last month's extra work

Check your log for days or hours beyond the allowance and add each as its own line with the date and rate. If the client used fewer days, note any rollover in the retainer line, for example "includes 1 day carried from October".

4. Handle a part month

If a retainer starts mid-month, prorate the first fee by working days. November 2026 has 21 working days. A retainer starting on Monday 16 November covers 11 of them, so the first invoice is £2,000 × 11 ÷ 21 = £1,047.62. Agree the method in advance; calendar days work too, as long as you both use the same one.

5. Send it before the period starts

Send it about a week before the month begins, with the due date on the first working day. Put a recurring reminder in your calendar so it never slips.

Billing a retainer with BillBee.work#

BillBee.work, a free invoice maker for freelancers, does not do recurring or scheduled invoices, so you still create each month's invoice yourself. What it does is make that a short job:

• Save the retainer on the client. Add a service with the fixed rate type, such as "Monthly retainer, up to 4 days", at £2,000. A fixed line is a flat amount, whatever the days.
• Save the overage rate too. Add "Additional day" as a daily service at £550. You can mix rate types on one invoice, so the retainer and the extra days sit side by side.
• Log the days as you go. Mark the days you work for the client on the service calendar, so at month end you can count them against the allowance. Extra days you pick for the daily line can print on the invoice as a work log.
• Switch on tax per invoice. If you set a named tax such as VAT at 20% on the client, it is applied to the subtotal when you turn it on.
• Set the due date. It defaults to 7 days after today; change it to the first working day of the period.
• Share the link. The client opens it without an account. On Pro, they can also download a PDF.

Be aware of the limits. There is no allowance or rollover tracking, so keep the count yourself and write any carry-over into the service name, for example "Monthly retainer, Nov 2026 (up to 4 days, 1 carried from Oct)". There is no notes or terms field either, so put the unused-time rule in the line description, and a general one-line payment note, such as "Payment due on the 1st by bank transfer", in your Payment Details, which print on every invoice. You mark each invoice paid yourself, and unpaid ones turn overdue automatically after the due date.

Tax notes for retainers#

Because a retainer is often paid before the work, the tax timing can differ from ordinary invoices. Keep it simple and check your local rules:

• UK VAT. For continuous supplies of services, HMRC says a tax point is created every time you issue a VAT invoice or receive a payment, whichever happens first. A November retainer invoiced on 23 October belongs in the VAT return covering 23 October.
• EU VAT. Where a service is paid for in advance, the European Commission explains that VAT is chargeable when the payment is received, on the amount received.
• US income tax. Under the cash method, the IRS says you include income in the year you actually or constructively receive it, and advance payments are generally reported in the year received. A January retainer paid in December usually counts in December's tax year.

If you are unsure, a short conversation with an accountant before the first retainer saves corrections later.

Common retainer invoicing mistakes#

A retainer works best when the invoice is boring: same day, same layout, clear period, extras listed separately. If you are weighing a retainer against charging by the day or the hour, day rate vs hourly rate compares the pricing models.

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