Work out the cost per run before you quote the job

The arithmetic that stops a fixed-price automation from quietly costing you money every month it keeps running. One formula, four inputs, done on the back of an envelope.

2026-07-14 · 4 min read

There is a specific way to lose money on a job that goes well.

You quote £3,000 to automate an invoice process. You build it, it works, everyone is pleased. It runs every day for the next two years. Somewhere in month four you notice you are paying for the API, the server, the error monitoring, and the twenty minutes a month it takes to unstick — and that nothing in the quote covered any of it, because the quote was for building the thing, and the thing does not stop after it is built.

The fix is one line of arithmetic done before the number leaves your mouth.

The formula

monthly cost = (runs per month × cost per run) + fixed monthly + (support hours × your rate)

Four inputs. Most people estimate the first and skip the other three.

Runs per month. Ask, do not assume. "How many invoices a day?" gets you a number the client believes. Then multiply their answer by three, because clients quote you a typical Tuesday and the system also runs on the last day of the quarter.

Cost per run. Everything one execution consumes:

Component	Example
Model call, ~4k in / ~500 out	£0.011
OCR on 3 pages	£0.004
Storage and egress	£0.001
Retries (assume 8% of runs go twice)	£0.001
Cost per run	£0.017

That last row matters more than it looks. Retries are not an edge case — they are a percentage, and if your pipeline has three model calls with a retry each, you are not paying for three calls, you are paying for three and a bit. Measure it after a week and replace the guess.

Fixed monthly. The server, the queue, the monitoring, the domain, the error tracker. It is usually £30–80 for something small, and it is usually forgotten entirely.

Support hours. The honest number is not zero, ever. Two hours a month at your rate. If you think it is zero, look at the last thing you shipped and count what it actually took.

Put a real job through it:

600 runs × £0.017 = £10.20
fixed monthly                = £45.00
2 support hours × £70        = £140.00
                             ─────────
monthly cost                 = £195.20

Nearly £200 a month, of which the API — the part everyone worries about — is a tenner. Over two years that is £4,685: more than the build fee, invisible in the quote, and coming out of your pocket.

What to do with the number

Now the quote has two components, and saying so is easier than people fear:

£3,000 to build it. £320 a month to run and support it, which covers the infrastructure, the API usage up to 1,000 documents a month, and any fixes needed. Above 1,000 documents it's 4p per document.

Three things are happening in that paragraph.

The margin is real. £320 against £195 of cost is 39%, which survives the month the client triples their volume without anyone renegotiating.

The usage band is stated. This is the single most useful sentence in any automation quote, because it converts an unbounded liability into a defined one. Without it, "we've started running the whole archive through it" is your problem. With it, it is a conversation about a number you already published.

The support is priced, not free. Two hours is in there. When the client asks for a change, you are not deciding whether to be generous; you are checking whether it fits in what they are already paying for.

The objection you will get, and the answer

"Can't we just do a one-off fee?"

You can, and sometimes should — a genuinely self-hosted thing on their infrastructure, with their API key, that you hand over and walk away from. That is a fine deal, and the honest version of it has three parts: they pay the running costs directly on their own account, you charge more for the build, and support afterwards is billed hourly at a rate you state now.

What does not work is the middle: your API key, your server, their volume, one payment. That is not a business model, it is a subscription you are paying on somebody else's behalf.

Do it now, not later

Before your next quote, fill in four numbers. It takes five minutes and it is the difference between a job that pays for two years and one that bills you for two years.

If it comes out worse than you expect, that is the arithmetic doing its job — better to find out on an envelope than in month four. Price the work runs the same calculation across retainers, per-seat pricing and value-based quotes, and includes the case where the honest answer is that the job is not worth doing at any price the client will pay.

Take it further

Price the work — Scope it, cost it, quote it — and know the number below which the job loses you money. (3 lessons, 80 min, 2 free)
Sell the thing, not the hours — Why your rate has a ceiling, where the repeatable part of your work is hiding, and what a product costs you after the sale. (3 lessons, 85 min, 1 free)