Key takeaways
What this article covers, in order:
- The invoice Hannah kept forgetting
- Decision 1: in advance or in arrears?
- Decision 2: what about extra work?
- Decision 3: how will payments be matched?
- The bookkeeping bit: money for work you haven't done yet
- A set-up checklist for every new retainer
A recurring invoice is one that goes out automatically on a schedule, for the same amount or the same items each time. A retainer invoice is the most common reason to use one: a client pays a fixed sum each month for a set amount of work or availability. Getting them right comes down to three decisions (billing in advance or arrears, what happens to extra work, and how payments get matched) plus one bookkeeping point about money received before the work is done.
The invoice Hannah kept forgetting
Hannah is a marketing consultant in Brighton with four retainer clients. Each pays £1,500 a month. In theory that's £6,000 a month of predictable income. In practice, she raised them by hand whenever she remembered, which was usually around the 8th, sometimes the 15th, once not at all until the client asked.
Her clients weren't paying late. She was billing late. Moving to scheduled invoices on the 1st of every month got her paid about a week earlier on average, with no extra effort. That's the whole case for recurring invoices in one paragraph.
Decision 1: in advance or in arrears?
In advance means you invoice at the start of the period for the work you're about to do. Common for retainers, subscriptions, rent, memberships and maintenance contracts. Your cash arrives before your costs. If the client stops paying, you stop working, and you haven't given away a month for free.
In arrears means you invoice at the end for work already done. Common for variable work, hourly billing and some larger clients who insist on it. It's fairer when hours fluctuate, but you're always lending the client a month.
For a fixed retainer, in advance is usually better for a small business. Agree it in writing at the start.
Decision 2: what about extra work?
Most retainers cover a set number of hours or deliverables. Decide what happens when the client goes over, before it happens.
Options:
- Overage billed separately at an agreed hourly rate, invoiced in arrears at month end.
- Rollover of unused hours to next month (generous, but can pile up).
- Hard cap, with extra work quoted as a separate project.
Here's Hannah's arrangement with one client: £1,500 a month in advance for up to 10 hours, extra hours at £90, billed at month end.
| Month | Retainer (in advance) | Hours used | Extra hours | Extra billed | Total invoiced |
|---|---|---|---|---|---|
| Oct 2026 | £1,500 | 13 | 3 | £270 | £1,770 |
| Nov 2026 | £1,500 | 9 | 0 | £0 | £1,500 |
| Dec 2026 | £1,500 | 12 | 2 | £180 | £1,680 |
| Total | £4,500 | 34 | 5 | £450 | £4,950 |
Each row checks out: 3 × £90 = £270, 2 × £90 = £180, and £4,500 + £450 = £4,950. The retainer goes out on the 1st as a recurring invoice; the overage is a separate one-off invoice on the last working day.
Keep the two separate. Clients' finance teams like a fixed retainer that's the same every month, and a separate, itemised extras invoice is much easier to approve than a retainer that's a different amount each time.
Decision 3: how will payments be matched?
A recurring invoice that's paid by standing order is wonderful, until the client changes the amount, misses a month or pays two at once. Make matching easy:
- Ask the client to use the invoice number as their payment reference.
- If they pay by standing order, check each month that the amount and date haven't drifted.
- Match each payment to the specific month's invoice, not just "the oldest one", so your aged debtors stays meaningful.
- If a payment covers two months, split it across both invoices.
The bookkeeping bit: money for work you haven't done yet
Here's where retainers catch people out. Say a client pays a quarterly retainer of £4,500 in advance on 1 Oct 2026, covering Oct 2026, Nov 2026 and Dec 2026.
In your bank, you have £4,500 on day one. But under accruals bookkeeping, you've only earned a third of it by 31 Oct 2026. The rest is money held for work you still owe. Until you do that work, it sits on your balance sheet as income received in advance (also called deferred income), which is a liability.
| Month end | Invoiced and received | Earned this month | Total earned so far | Still held as received in advance |
|---|---|---|---|---|
| 31 Oct 2026 | £4,500 | £1,500 | £1,500 | £3,000 |
| 30 Nov 2026 | £0 | £1,500 | £3,000 | £1,500 |
| 31 Dec 2026 | £0 | £1,500 | £4,500 | £0 |
By 31 Dec 2026 the full £4,500 has been earned, and the amount held in advance is back to zero. At each month end, earned so far plus still held always equals £4,500.
Does a tiny business need to do this monthly? Not always. If you invoice monthly in advance for the month you're in, the timing is close enough that most people don't bother. Where it matters is quarterly or annual billing, and especially at your year end, when a large up-front payment could otherwise make the year look more profitable than it was. Your accountant can set up the year-end adjustment if you're not sure. It's a quick conversation, and worth having before the year closes.
A set-up checklist for every new retainer
- [ ] Written agreement: fee, what's included, notice period
- [ ] Billing date (we like the 1st) and payment terms
- [ ] In advance or in arrears, agreed in writing
- [ ] Rate and process for extra work
- [ ] Recurring invoice scheduled, with a clear description and the period it covers ("Retainer for Nov 2026")
- [ ] Client's finance contact and any PO number on the invoice
- [ ] Payment reference agreed
- [ ] End date or review date in your diary
- [ ] Price review date (an annual increase is normal; tell the client well in advance)
When a retainer ends
Stop the recurring invoice the moment notice is given. It's surprisingly easy to send one more invoice after a client has left, and a credit note plus an apologetic email is an awkward way to finish a working relationship. If you've been paid in advance for a period you won't now deliver, agree whether to refund or complete the work, then record it accordingly.
How HelloBooks helps
Recurring invoices are on HelloBooks Pro (£14.99/month). You set the schedule and the invoice goes out on time, every time. Free includes invoices, quotes, unlimited email payment reminders and AR ageing, so you can still run retainers by hand on Free if you only have one or two.
When the client pays, the money comes in through your Open Banking bank feed or a CSV statement and appears on the reconcile screen with an AI match suggestion against the right invoice. You confirm, or change it if they've paid two months at once. See recurring invoice for more, freelancers can look at this page, and plan details are on pricing.
FAQs
What's the difference between a recurring invoice and a retainer?
A recurring invoice is the mechanism: an invoice that's generated automatically on a schedule. A retainer is the commercial arrangement: a client paying a regular fee for ongoing work or availability. You use recurring invoices to bill retainers, subscriptions, rent and similar.
Should retainers be billed in advance?
For fixed retainers, billing in advance is common and protects your cash flow. Billing in arrears suits variable work. Whatever you choose, agree it in writing at the start.
Is a retainer paid in advance income straight away?
Under accruals bookkeeping, only the part you've earned is income. The rest is held as income received in advance until you do the work. For monthly retainers billed for the current month, the difference is usually small; for quarterly or annual payments, it's worth getting right.
How should I bill extra hours on a retainer?
Most small businesses bill extra hours separately at month end, at an agreed hourly rate. It keeps the regular retainer invoice the same every month, which clients' finance teams appreciate.
What if the client pays by standing order?
That's fine, and often convenient. Still match each payment to the specific invoice it pays, and check each month that the amount hasn't changed. Standing orders don't update themselves when your fee goes up.
Set it up once, carefully, and let the 1st of the month do the rest.
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