14 invoices recorded for under 5p each
One £150 invoice from an AI model provider arrived in the books at 20% UK VAT, flagged for review, with no receipt attached. The PDF said otherwise: a UK VAT number, no VAT charged and a reverse-charge note. It belonged at 0%.
Software billed from abroad is where VAT gets awkward. A supplier outside the UK that charges no VAT is usually reverse charge, and which way an invoice goes depends on what the PDF actually says. The accounting system makes its own guess at each one, and the guess can be wrong.
Before the agent, their accountants answered each case like this one email at a time. The agent's job was to take those answers and apply them the same way, every time.
An agent that works from the accountants' own answers, written down as 7 rules. Each run went through the same steps, in the same order.
7 written rules from their accountants and the business, read in full before anything else.
Supplier invoice PDFs from 9 days back, so nothing slipped between one run and the next.
The supplier, amount, currency, date, VAT number and the VAT actually charged.
In a fixed order, every time. Each entry names the rule it was recorded under.
Matched to the payment from the business bank account.
The invoice PDF goes on the entry. No PDF, no entry.
Anything the rules do not cover, with the reason and the PDF.
What it recorded and under which rule, what it skipped and why.
The rules were the approval. Routine invoices the rules covered, it recorded itself, under a standing instruction from the business. Anything new or unclear went to a person first.
Up to 29 October 2026, an AI bookkeeping agent recorded 14 supplier invoices for under 5p each in AI model costs, against about £2.54 each for a bookkeeper doing the same work by hand.
| Measure | AI bookkeeping agent | Bookkeeper by hand |
|---|---|---|
| Cost per invoice | Under 5p | About £2.54 |
| What the cost counts | The AI model's usage on every run | 9 minutes at £16.92 an hour |
| Receipt on the entry | On all 14 | Up to the bookkeeper |
| Rule named on the entry | On all 14 | Up to the bookkeeper |
The agent's figure is what the AI model cost across every run from 21 August to 29 October 2026, including runs with nothing to record, divided by the 14 invoices. Two August runs logged no cost, so each is counted at the price of the dearest run on record, which makes the figure an upper limit. It does not count building the agent or looking after it. The bookkeeper's figure is our own sum: the 9 minutes a government estimate puts on receiving, entering and checking one purchase invoice, at the £16.92 median hourly pay of a UK bookkeeper in 2026. Each of the 14 invoices was matched to its payment from the business bank account.
Under 5p an invoice in AI model costs, on this agent's record: up to 29 October 2026 it recorded 14 supplier invoices, against about £2.54 each for a bookkeeper doing the same work by hand. That counts the model's usage on every run, with the two August runs that logged no cost counted at the dearest run's price, and not building the agent or looking after it.
About 9 minutes to receive, enter and check one purchase invoice, on a government estimate. At the £16.92 median hourly pay of a UK bookkeeper in 2026, that is about £2.54 an invoice.
It can when it works from written rules. This agent read each invoice PDF and applied its accountants' rules in a fixed order, and a £150 invoice the accounting system had put at 20% UK VAT went into the books at the 0% reverse charge the PDF showed. Anything the rules did not cover went to a person.
It is when it works inside safeguards. This agent never guessed, worked only from the written rules, never recorded anything twice and attached the receipt to every entry it recorded. Anything new or unclear went to a person first.
This is the agent behind AI invoice processing, and the kind of work we build agents for in accounting practices. The agent most businesses start with is the AI receptionist, and how we work and what it costs is on one plain page.
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