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The problem
A retainer is recurring revenue billed like one-off work
An agency retainer is a fixed monthly or quarterly fee for an agreed scope, often with hours or deliverables above it billed on top. In practice each month's invoice is raised by hand from a spreadsheet of what was delivered, the overage is added from a time tracker, and the set-up fee and the campaign milestone agreed in the SOW live in someone's memory. The retainer is predictable revenue; the billing of it isn't.
UK agencies wait longest: late payment costs UK businesses almost £11bn a year and 86 hours each in chasing (London Economics, 2025), and in the FSB and GoCardless 2025 report 24% of small businesses were paid up to 60 days late. Statutory interest of 8% over base under the Late Payment of Commercial Debts Act only helps if the invoice went out on time with your terms on it.
Retainers · OctoberBy hand
Retainer invoices due1 Oct
18
Raised by the 1st
7
Overage not billedhours logged
41 h
What Fynex runs
How retainer billing runs on Fynex
One contract per client; the calendar raises the invoices.
Recurring billing
Recurring retainer invoices on the contract calendar
Monthly, quarterly or any custom cadence, with notice periods and auto-renew — recurring billing on the contract. Each period's retainer invoice is issued exactly once, on the day, numbered in a gapless series — whoever is on holiday.
Overage
Hours and usage above the retainer
Send hours or deliverables as usage events or a CSV from your time tracker. An included allowance covers the retainer; anything above it is rated at your overage rate and lands on the same client's invoice at period close.
Hybrid contracts
Set-up fees and milestones on the same agreement
The onboarding fee bills once, the campaign milestone bills on sign-off, and the retainer keeps running — one contract, versioned, so a change of scope is an amendment rather than a new spreadsheet row. More on deposits and stage payments.
Collections
Paid on a link, booked to your books
Each invoice carries a hosted payment link for card, or the invoice number as the Faster Payments reference. Your payment terms and late-payment wording are on the invoice, and every payment is matched to it in Xero or QuickBooks.
Retainer · Riverside & Co
October retainer
£6,000
Overage · 12 h
£1,800
Statusissued 1 Oct
Paid
How we compare
The same job, with the leaks closed
Point tools solve part of it. Fynex runs the whole thing on one platform.
The problem
Other platforms
Recommended
!Raise the monthly retainer invoice
✕Other platformsA repeating invoice template, edited by hand each month.
✓FynexIssued from the contract calendar, exactly once per period.
!Bill hours above the retainer
✕Other platformsCopied from the time tracker onto the invoice.
✓FynexUsage events or CSV rated against an included allowance.
!Bill set-up fees and milestones
✕Other platformsSeparate one-off invoices someone remembers to raise.
✓FynexOn the same versioned contract, each on its own trigger.
!Collect and reconcile
✕Other platformsBank transfer, matched by hand.
✓FynexPayment link or transfer with the invoice number as reference, matched automatically.
FAQ
Questions, answered
Retainer billing invoices a client a fixed recurring fee — usually monthly or quarterly — for an agreed scope of work, sometimes with an allowance of hours or deliverables and overage billed above it. It gives an agency predictable revenue, provided the invoices go out on time and the overage is actually billed — the practical side is in raise and chase the monthly retainers.
Track the hours, compare them with the retainer's allowance, and bill the excess at an agreed overage rate on the next invoice. In Fynex, hours arrive as usage events or a CSV; the retainer's included allowance is applied first and the rest is rated automatically onto the client's period-close invoice.
Yes. A Fynex contract can carry a recurring retainer, usage above an allowance, one-off fees and milestone payments, each billed on its own schedule. An amendment adds a new contract version, so every invoice traces back to the scope it was billed against.
Under the Late Payment of Commercial Debts (Interest) Act 1998 a UK business can claim statutory interest of 8% over the Bank of England base rate on late B2B invoices, plus fixed compensation of £40, £70 or £100 depending on the debt. Fynex puts your payment terms and late-payment wording on every invoice and issues it on the due date, so the clock starts when it should. The escalation that follows: late-payment letters that work.
Yes. Invoices and payments sync to Xero and QuickBooks, each payment matched to the invoice that raised it, so the retainer revenue in your books is what was actually billed and collected. If contractors deliver part of the retainer, see rebilling contractors. Developers: the subscriptions reference.
Keep building
The rest of the agency billing layer
Every guide below runs on the same contracts, invoices and payouts. Start with one, or run the whole stack.
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FCA-authorised EMI
An e-money institution via Fondy. We can hold and move your funds.
Licence
E-money institution
FCA
Client funds
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Card data
PCI DSS
Level 1
Encryption
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Audit logs
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Activity
Payout · £23,84714:02:11
Logged
Split · ORD-2024-00114:02:09
Logged
Built-in KYC / KYB
The switch that turns the business on.
Verification
KYB · Northwind Labs Ltd
Approved
KYC · J. Whitfield
Approved
We do Fridays so you don't have to.Payouts at midnight. You, asleep.Invoices that chase themselves. Ruthlessly.We carry the chargebacks. You carry on.We do Fridays so you don't have to.Payouts at midnight. You, asleep.Invoices that chase themselves. Ruthlessly.We carry the chargebacks. You carry on.We do Fridays so you don't have to.Payouts at midnight. You, asleep.Invoices that chase themselves. Ruthlessly.We carry the chargebacks. You carry on.
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