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Part 1 of 7 · Menu cost calculator series ~6 min read

A menu cost calculator on AWS for a few dollars a month

A dish is costed once, when the menu is written, using the prices from that week and the weights from the recipe. Eighteen months later beef has moved, the portion has crept, and nobody has recosted anything because recosting forty dishes by hand is a day’s work. The gross profit has fallen four points and the reason is invisible.

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Photo by Robinson Greig on Unsplash

Key takeaways

  • Yield turns purchase price into usable price, and it is often a large adjustment.
  • Every costing is stamped with the date and the exact prices used.
  • Portion variance usually moves food cost more than ingredient prices do.
  • Report cash margin alongside gross profit percentage, always.
  • Designed on AWS for about $2 a month.

The whole system on one page

Before any code, here is the shape of what we are designing.

System: purchase prices turned into dated plate costsThree boxes across the top sit outside the AWS account. On the left, Invoices carrying this week's prices. In the middle, Recipes and measured yields. On the right, Whoever prices the menu. Each connects by an arrow to the AWS account container below. Prices flow down into the account. Quantities and yields feed in. Costs, dated, go back out. Inside the AWS account are three components in a row. On the left, Usable cost, the purchase price adjusted for yield. In the middle, Plate cost per portion, stamped with a date. On the right, the Report, showing margin and percentage alongside what sells. A note at the bottom says the first box is where most of the error in hand-costing lives.AWS ACCOUNTInvoicesthis week's pricesRecipesand measured yieldsWhoever pricesthe menuUsable costpurchase priceadjusted for yieldPlate costper portion,stamped with a dateReportmargin and %,and what sellspricesquantities andyieldscosts, datedThe first box is where most of the error in hand-costing lives.
Fig 1. Three things outside the account, three pieces inside it. The yield adjustment in the first box is the one most hand-written costings omit entirely.
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Three adjustments

Between the invoice and the plate there are three things that move the number, and hand-written costings typically include one of them.

  • Yield. A whole beef fillet loses weight to trim; potatoes lose weight to peeling; a lettuce loses its outer leaves. The usable kilo costs more than the purchased kilo.
  • Cooking loss. Meat loses weight in the pan, sauces reduce. A hundred and eighty grams on the plate is more than a hundred and eighty grams raw.
  • Waste and trim value. Some trim becomes stock or staff food and has value; most is a cost. The treatment should be stated rather than assumed.

What runs (the inside)

  • Usable cost. Applies measured yields to purchase prices, per ingredient. Part 2.
  • Plate cost. Assembles a dish from its recipe at a point in time, stamped. Part 3.
  • The report. Dish-level profitability, with the two numbers that have to appear together. Parts 4 and 5.

One dish, end to end

One dish costed from purchase price through yield to plate costA horizontal row of five boxes joined by arrows. Beef at eleven pounds a kilo as purchased. Yield sixty-eight per cent, giving a usable price of sixteen pounds eighteen a kilo. One hundred and eighty grams on the plate equals two pounds ninety-one. Plus the rest equals four pounds sixty-two total. Sells at nineteen pounds fifty, a gross profit of seventy-six per cent and a margin of fourteen pounds eighty-eight. A note says costed on purchase price alone it looks like three pounds sixty-eight, which is a twenty per cent error.ONE DISH, END TO ENDBeef at £11.00/kgas purchasedYield 68%usable: £16.18/kg180g on the plate= £2.91Plus the rest= £4.62 totalSells at £19.50GP 76%, margin £14.88Costed on purchase price alone it looks like £3.68. That is a 20% error.
Fig 2. The same dish as one line. The yield step in the second box is worth nearly a pound on this plate and is the step most often skipped.
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In plain words

Beef comes in at eleven pounds a kilo. The kitchen weighed a delivery, trimmed it, and weighed what was usable: sixty-eight per cent. So the usable cost is eleven divided by nought point six eight, which is sixteen pounds eighteen a kilo.

A hundred and eighty grams on the plate costs two pounds ninety-one at that rate, against one pound ninety-eight if you use the purchase price. Add the potatoes, the sauce, the garnish and their own yields and the dish costs four pounds sixty-two.

At nineteen fifty it makes fourteen pounds eighty-eight and runs at seventy-six per cent gross profit. Both of those numbers matter and the last post is about why reporting only one of them leads to bad menu decisions.

Design rules that shaped every decision

  • Yields are measured in the kitchen, not taken from a book.
  • Every costing stores the exact prices used and the date.
  • Recipes are versioned; changing a recipe does not rewrite history.
  • Report cash margin and percentage together, always.
  • Never automatically change a menu price.
  • Say when a costing is stale, rather than quietly using old prices.

Why this shape

Recipe costing is done once and then not again, because doing it by hand is slow and the result goes out of date within a month. The consequence is that most kitchens are operating on costings that were correct at some point in the past and have drifted by an unknown amount.

Automating the arithmetic is not the hard part. The parts that matter are getting yields measured once properly, keeping the price history so a change can be attributed, and presenting the result in a way that does not encourage the two classic errors: chasing gross profit percentage, and removing dishes that look unprofitable.

The next four posts walk through each piece: how yield turns purchase price into plate cost, why prices need a date stamped on them, why portion size moves more than price does, and how to read a dish profitability report without getting it wrong. One diagram per post, a cost breakdown, and an engineering reference at the end.

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