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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.
US B2B buyers stretch terms: average terms are 45 days and 43% of the value of B2B credit invoices is overdue (Atradius US 2025), and 56% of US small businesses are owed money, about $17,500 each (QuickBooks 2025). An invoice raised on the 6th instead of the 1st is five days of that on top.
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 ACH reference. A saved card is charged next cycle, and every payment is matched to its invoice in QuickBooks or Xero.
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.
By card on the invoice's hosted payment link — saved for the next cycle if they choose — or by ACH bank transfer with the invoice number as the payment reference. Checks were still 26% of US B2B payments in 2025 (AFP), which is why the link and the reference matter: the payment arrives already matched to its invoice. When they pay late anyway: Net 30 but paid in 90.
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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Activity
Payout · $23,84714:02:11
Logged
Split · ORD-2024-00114:02:09
Logged
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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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