Friday at six is not the moment to discover your fish supper is underpriced. By then the batter is mixed, the fryers are up to temperature and there are fourteen tickets on the rail. Portion cost is a decision you make at the prep bench on a quiet Tuesday, with a set of scales and a calculator — not in the middle of a rush.

Most shops have a decent idea what they pay for a box of fish. Far fewer know what a single portion costs once trimming, batter, oil, chips and packaging are added in. That gap is where gross profit leaks away, a few pence at a time, hundreds of suppers a week.

Why yield matters more than invoice price

The price on the delivery note is not the price of your fish. What matters is the cost per usable kilo — after trimming, after the ragged ends, after the bits that go in the bin or into fish cakes.

Say one supplier quotes £10 per kilo and you lose a fifth of it to trim. Your usable cost is £10 ÷ 0.80, so £12.50 per kilo. Another supplier quotes £11 per kilo but trims clean, losing only eight per cent. That works out at £11.96 per usable kilo. The cheaper invoice is the dearer fish. Run this comparison properly at least once a year, and again whenever a supplier changes.

The five things in a fish supper box

Every portion is made of five separate costs, and each one deserves its own line in your costing sheet:

• Fish — priced by usable weight after trimming, not by the weight you bought.
• Chips — the potato, plus the loss from peeling, trimming and the water that cooks out in the fryer.
• Batter — flour, raising agent, seasoning and water. Cost the batch, then divide by the number of portions it coats.
• Frying oil — the drum or block price divided by the number of portions you fry before you change it.
• Packaging — box, paper bag, napkin, fork, salt sachet, and any branded label or sticker.

Anything else that leaves the counter — mushy peas, curry sauce, a can of pop — should be costed as its own line and never buried in the fish price.

A fish supper costed to the penny

Here is the method, step by step. Swap in your own invoice figures; the arithmetic stays the same.

1. Fish. Fillet costs £12 per kilo on the invoice. You lose ten per cent to trim, so usable cost is £12 ÷ 0.90 = £13.33 per kilo. A 150g raw portion therefore costs £2.00.
2. Chips. A 20kg bag of potatoes at £14 gives 70p per kilo. Peeling and trimming lose twenty per cent, so usable cost is 87.5p per kilo. A 380g raw weight yields roughly a 300g cooked portion, costing 33p.
3. Batter. A batch costs £1.60 and coats 24 portions. That is 7p per portion.
4. Oil. A 20-litre drum costs £30 and you fry around 600 portions before changing it. That is 5p per portion.
5. Packaging. Box 12p, bag 4p, napkin 1p, fork 7p, sachet 1p — 25p.

Add those up and your plate cost is £2.70. That figure is your foundation. Everything else — energy, wages, rent, card fees — comes out of what is left after the ingredients.

The price on the board is a promise. The grams on the scale decide whether you keep it profitably.

The oil line most shops get wrong

Oil is not a fixed overhead you can shrug at. It is a variable cost per portion, and it moves the moment your frying practice changes.

Change the oil early because it is darkening and your cost per portion climbs. Stretch it too far and the fish tastes of last night's scampi, the batter browns too fast and customers notice. Find the sweet spot and write it down: how many portions per change, per fryer, on a normal week. Then re-check it when you change batter recipe or add a new fried line.

From portion cost to a price on the board

You need one more decision before you can price anything: what share of the selling price should ingredients take? Set your own target based on your rent, wages and energy bills, then do the division.

• Portion cost £2.70, target ingredient cost 30% → £2.70 ÷ 0.30 = £9.00.
• Same portion, target 35% → £2.70 ÷ 0.35 = £7.71.

If you are VAT-registered, the price on the board includes VAT, so work from the net figure. At a 20% rate, a £9.00 board price leaves £7.50 of net revenue — which pushes your ingredient share up to 36%. Hot takeaway food is standard-rated in the UK, but the rules have awkward corners, so confirm your own position with your accountant rather than guessing.

Then sanity-check the result against your local market. If your maths says £11 and every shop on the parade charges £8, you have a problem to solve — smaller portions, a cheaper cut, a different supplier, or a better story about quality. What you must not do is price off the competition and hope the margins sort themselves out.

Keeping the number honest

A costing done once is a snapshot, not a system. Prices move, yields drift, and a new fryer cooks differently from the old one.

• Re-cost when an invoice moves. Any change of more than a few per cent on fish, potatoes, oil or packaging deserves a fresh calculation.
• Weigh portions weekly. Digital scales on the prep bench, standard portions bagged ahead of service. Eyeballing a fillet is how a 150g portion becomes 190g.
• Watch the bin. A sudden jump in trim waste usually means a change in supplier, staff or knife skills.
• Keep one costing sheet per dish. One page, current prices, dated. If a supplier asks why you are switching, the sheet answers them.

Do this and the fish supper stops being a guess. You will know, to the penny, what leaves the fryer and what stays in the till — which is the only way to argue about price with a clear head.

Photo: makafood / Pexels