AI agents for business finance: what they can and can't do
What AI agents can do in bookkeeping, close, collections and compliance today, where a person must stay in charge, and how to judge a product.
The short answer
Invoice each quarter before it starts, with payment due before work begins; define the scope and an hours cap; fix the currency and who pays transfer charges; and agree whether the fee is grossed up for Nigerian withholding tax, which PwC lists at 10% for non-residents on professional fees. Add notice, rollover and late-payment terms so the arrangement survives a slow month on either side.
Nigerian start-ups often prefer retainers to project fees: they get steady access to a designer, developer or marketer without hiring. For a UK freelancer, a quarterly retainer can be the most stable income you have, or a slow leak of unpaid hours. The difference is in the terms you set before the first invoice.
Payment in advance, per quarter
The core term is simple: the fee for a quarter is invoiced before it starts and paid before work begins. That protects you against the start-up that runs short of cash mid-quarter, which is common in early-stage companies between funding rounds.
- Invoice date: for example 15 days before the quarter starts (example; choose your own).
- Due date: on or before day one of the quarter.
- Consequence: if unpaid by the due date, work pauses until payment arrives, and the quarter is not extended.
If the client will not pay a full quarter up front, monthly in advance is the usual compromise. Paying in arrears for a retainer leaves you funding the client.
Scope and hours
A retainer without a scope becomes "can you just". Set out:
- What is included (for example "up to 40 hours per quarter of product design and design-system upkeep").
- What is excluded (new brand identity, out-of-hours support, paid media spend).
- How unused hours are treated: lost at quarter end, or rolled into the next quarter up to a cap.
- How extra hours are charged, and that they need written approval before you start.
- Response times, so "retainer" does not quietly mean "on call".
Currency, transfer costs and withholding tax
Currency
Decide whether the fee is in pounds, dollars or naira. A naira fee moves your costs into the client's currency risk; a pound fee moves it to the client. Whatever you choose, write it down, along with the date on which any conversion rate is fixed.
Who pays transfer charges
International transfers can carry charges at both ends and at intermediary banks. State that the invoice must arrive in full, with the sender bearing all charges, if that is what you want.
Withholding tax
PwC's Nigeria summary (reviewed 29 May 2026) lists 10% withholding tax for non-residents on commission, consultancy, technical, management and professional fees, as a final tax. Decide whether your fee is net or gross.
Worked example (illustrative). You want £4,500 a quarter in hand.
| Basis | Invoice | WHT at 10% | You receive |
|---|---|---|---|
| Fee stated gross | £4,500 | £450 | £4,050 |
| Fee grossed up | £5,000 | £500 | £4,500 |
£4,500 ÷ 0.9 = £5,000. Ask for the WHT receipt each quarter; it is the evidence for any UK credit. See Nigerian WHT on a UK freelancer's invoice.
Other terms worth writing in
- Notice: for example one full quarter's notice by either side, or the current quarter plus 30 days (example terms).
- Late payment: if UK law governs the contract, the Late Payment of Commercial Debts (Interest) Act can add statutory interest of 8% plus Bank of England base rate between businesses, unless the contract sets a different rate. Section 12 can exclude contracts with no significant UK connection, so a contractual interest clause is safer.
- Intellectual property: under the Copyright, Designs and Patents Act 1988, s.90(3), an assignment of copyright must be in writing and signed by the assignor. Tie the assignment to payment, so work transfers once each quarter is paid.
- VAT: ACCA's guidance explains that business-to-business services to a customer belonging outside the UK are generally outside the scope of UK VAT under the general rule; keep evidence that the client is a business.
- Governing law and disputes: name the law and a route (negotiation, then mediation, then a named court or arbitration).
Write the conversion date into the contract too: if a naira invoice is converted at the rate on the invoice date, and the client pays three weeks later, the gap is a cost one side carries. Saying which side in advance removes an argument.
Reviewing the retainer
Put a review point in the contract, for example at the end of every second quarter, where both sides look at hours used, what was delivered and whether the fee still fits. Start-ups change quickly: the founder who hired you for design may need product strategy six months later. A scheduled review lets you reprice or reshape the work without it feeling like a renegotiation forced by a crisis, and it gives the client a natural moment to raise concerns before they turn into a dispute.
Where Pryme fits
Pryme invoicing and a Business Account with local GBP, USD, EUR and NGN details let a Lagos client pay a quarterly invoice in whichever currency you agreed, and the money stays in that currency until you Swap it. For taking money up front on project work, see deposits from Nigerian clients, and for interest on late quarters, late payment interest.
Questions people ask
Should a retainer be paid in advance?
Yes, usually. Invoice before the quarter starts and pause work if payment has not arrived by day one.
Do Nigerian clients deduct tax from a retainer?
Often. PwC lists 10% WHT for non-residents on professional and consultancy fees. Agree whether your fee is grossed up.
Do I charge UK VAT on a retainer for a Nigerian company?
Business-to-business services to a customer outside the UK are generally outside the scope of UK VAT; keep evidence the client is a business.
What happens to unused retainer hours?
Whatever the contract says. Decide in advance whether they lapse or roll over up to a cap.
Sources
- PwC Worldwide Tax Summaries: Nigeria, withholding taxes (reviewed 29 May 2026) · accessed Oct 2026
- GOV.UK: Late commercial payments, interest and debt recovery (updated 16 Oct 2026) · accessed Oct 2026
- legislation.gov.uk: Late Payment of Commercial Debts (Interest) Act 1998, section 12 · accessed Oct 2026
- legislation.gov.uk: Copyright, Designs and Patents Act 1988, section 90 · accessed Oct 2026
- ACCA In Practice: VAT on supply of services to customers outside the UK (Sept 2022, modified 23 Feb 2024) · accessed Oct 2026
This article is general information, not financial, legal or tax advice. Products described are provided under the terms on this site and are subject to regulation and eligibility.