margin-checker

---
name: margin-checker
description: Works out true contribution per job, dish or product from your own sales and cost lines, ranks them by the pounds they actually earn, and names every cost that is missing.
---

# Find out which jobs, dishes or products actually make you money

You paste in what you sold and what it cost you. You get back a ranked list of what each line really contributes in pounds, and a plain list of the costs you did not give me.

## What it does

1. **Take the two lists in whatever shape they arrive.** A sales list (item name, price charged, units sold, period) and a cost list (what one unit costs you to deliver). Accept a paste, a CSV, an export, a photo of a spreadsheet or a typed list. Never send the owner away to reformat first, and never start work on only one of the two lists.
2. **Strip VAT out of every selling price before calculating anything.** UK standard rate is 20%, so a £12.00 menu price is £10.00 of net sales (gov.uk VAT rates). Rates differ by line: most food sold in a shop is zero-rated while hot takeaway and eat-in food is standard-rated, so ask which rate applies to each group rather than applying one rate to the lot. A margin worked on a VAT-inclusive price overstates profit by the whole VAT amount.
3. **Build contribution per unit, not a gross profit percentage.** Contribution equals net selling price minus the costs that exist only because that item was sold: ingredients, materials, the subcontractor, the delivery, the card fee. Rent, wages, insurance and van costs stay out at this stage. This is the definition the menu engineering method uses, price excluding sales tax minus cost per serve.
4. **Multiply contribution by volume and rank the list on total pounds, not on margin percentage.** Openaccountant's pricing-optimizer skill puts the trap plainly: a 30% margin on a £10,000 job earns £3,000 while a 60% margin on a £500 job earns £300. Percentage ranking flatters small items and hides the ones paying the bills.
5. **Name every cost you were not given and mark that line INCOMPLETE.** Never substitute zero, never estimate, never borrow an industry figure. Anthropic's own margin-analyzer skill makes this explicit: if the accounting data shows no cost of goods sold, do not use zero as the cost input, go back and ask for a cost breakdown per line. An incomplete line is excluded from the ranking and listed separately.
6. **Split the finished list into four groups using the owner's own averages as the dividing line, never an industry benchmark.** High volume and high contribution, high volume and low contribution, low volume and high contribution, low volume and low contribution. Work out a separate average for each section (starters against starters, callouts against installs) so like is compared with like.
7. **Flag any line contributing under 20% of its net price as a data point, not a verdict.** That is the threshold Anthropic's margin-analyzer uses. Say what the number is and what it would take to move it. Do not attach an instruction to it.
8. **Show the price that would hit a margin the owner names, using target price = unit cost divided by (1 minus target margin).** A £350 cost at a 50% target is £700. Present it as arithmetic the owner can act on or ignore. Do not recommend a price: the pricing decision depends on competition and customer relationships that are not in the data.
9. **Hand back one table plus a Data Quality section.** The table carries item, units, net price, unit cost, contribution per unit, total contribution, and group. The Data Quality section lists every incomplete line and the single number that would fix each one.

## Then it checks

1. Every sales line has either a matching cost line or the label INCOMPLETE. No line silently carries a cost of zero.
2. The arithmetic closes: the sum of contribution across all complete lines equals total net sales minus total direct costs, to the penny.
3. Every price used is VAT-exclusive, and the report states which VAT rate was applied to each group and who confirmed it.
4. The ranking is by total pounds of contribution, and the report says so in a sentence, so nobody reads it as a percentage ranking.
5. No sentence in the output tells the owner what to charge.
6. Every figure traces back to a line the owner supplied. Nothing was filled in from an average, a benchmark or a guess.

Any check fails: name it, redo that step once. Failed twice: say what is wrong and stop.

## Rules
- Public information only.
- Never invent a fact, a number or a quote.
- Never fill a missing cost with zero, an estimate or an industry average. An incomplete line is reported as incomplete and left out of the ranking.
- Contribution is not profit. Rent, wages, insurance, software and finance costs are not in these numbers, so a positive contribution does not mean the business made money that month. Say this in the output every time.
- This is analysis, not pricing advice and not tax advice. VAT treatment on any line, and anything that changes the tax position, is for the owner's accountant to confirm before it is acted on.
- Do not recommend a price. Show the target-price arithmetic and the ranked list, and let the owner decide.

## Built from
- Anthropic, "Claude for Small Business", https://www.anthropic.com/news/claude-for-small-business, published 13 May 2026: names a margin analyzer among its fifteen ready-to-run workflows and sets the approval posture this skill copies, the owner approves the plan first.
- anthropics/knowledge-work-plugins, small-business plugin, margin-analyzer skill, https://github.com/anthropics/knowledge-work-plugins/blob/main/small-business/skills/margin-analyzer/SKILL.md, 23,911 stars: the refusal to treat a zero cost figure as a real cost, the 20% margin flag as a data point rather than a recommendation, and the hard scope boundary it states as "This skill surfaces data. It does not recommend a price."
- openaccountant/skills, pricing-optimizer and client-profitability skills, https://github.com/openaccountant/skills, 66 stars: the target price formula (unit cost divided by one minus the desired margin), ranking by total profit contribution rather than margin percentage, and the warning that an unattributable expense belongs in overhead rather than being spread onto an item.
- Kasavana and Smith menu engineering matrix, as set out by Loaded, https://www.loadedhub.com/resources/menu-engineering-matrix-restaurant: contribution margin defined as selling price excluding sales tax minus cost per serve, the four-group split, and the instruction that the midpoint on each axis is the owner's own menu average and that each section gets its own average.
- GOV.UK, "VAT rates on different goods and services", https://www.gov.uk/vat-rates: the 20% standard rate, 5% reduced rate and 0% zero rate, and the fact that rates differ line by line, which is why VAT is stripped per group and not with one blanket rate.