Why it helps
Supplier prices change all the time, and it's easy for a popular dish to quietly stop making money. Working out what a plate actually costs means converting pack prices to per-gram costs, adding them up, then taking GST out of your menu price before you compare. It's fiddly, so it often doesn't get done.
AI can lay out the whole calculation for you: cost per ingredient, cost per plate, food cost percentage and gross profit at a few different prices. The catch is that AI can make arithmetic slips, so you ask it to show its working and you check the numbers, ideally in a spreadsheet.
The prompt
Copy it, swap the bits in [square brackets], and paste it into ChatGPT, Claude, Gemini or Copilot.
I run a [cafe / restaurant / food truck] in New Zealand. Help me cost one dish and look at menu price options. Use NZ English. For each ingredient I give you: 1. Work out the cost per gram (or per unit) from the pack price and pack size. 2. Work out the cost for the portion I use. 3. Add them up for a total cost per plate. Then: - My menu prices include GST at 15%. For each price option, work out the price excluding GST (divide by 1.15). - Show the food cost as a percentage of the ex-GST price, and the gross profit per plate in dollars. - Do this for these price options: [e.g. $16.50, $17.50, $18.50 incl GST]. - Also tell me what price incl GST would give a food cost of [my target, e.g. 30]%. Rules: - Show your working for every step, so I can check it. - Only use the prices and portions I give you. Don't invent any costs. If something's missing, tell me. Dish: [name] Ingredients (pack price, pack size, portion used): [list]
Then keep chatting
Lay this out as a table I can paste into a spreadsheet, with formulas instead of fixed numbers.
Add 5% for waste and trim and show the new results.
My brie has gone up to $[price] per kg. Redo the numbers.
Which ingredient makes the biggest difference to the cost?
Step by step
- Pick one dish. Write down each ingredient, the pack price you pay (say if it's incl or excl GST), the pack size and how much goes on one plate. Weigh a few portions if you're not sure.
- Paste the prompt with your list and the price options you're thinking about.
- Check the working line by line. Better still, ask for a spreadsheet version and let the formulas do the maths.
- Compare the food cost percentage with your own target. Your accountant can help you set a sensible one for your business.
- Decide the price yourself, update the menu, and redo the costing whenever a key supplier price changes.
Worked example
Example details are made up. Your results will vary, so always read and check before you use them.
Watch out for
- AI can make arithmetic slips, even when it sounds sure. Always ask it to show its working, check a couple of lines with a calculator, or put it into a spreadsheet.
- Be clear about GST. Compare excl GST costs with excl GST prices. If you're not GST registered, tell the AI, because the comparison changes. Check ird.govt.nz or your accountant if you're unsure.
- The price on your menu should be the full price customers pay, including GST. The Fair Trading Act covers misleading pricing, so check consumerprotection.govt.nz if you add surcharges like a public holiday surcharge.
- Food cost is only part of the picture. Wages, rent and power matter too, so use this to compare dishes, not as your whole pricing plan. You don't need to share supplier names or negotiated rates; rough figures still work.
Go further
Cost your top five sellers first, as they make the biggest difference. Keep them in one spreadsheet so you can update a supplier price once and see every dish change. If a price needs to go up, the [price increase notice](/use-cases/price-increase-notice) use case can help you tell your regulars.
