How to Work Out Cost Per Portion

Use What You Use, Not What You Bought

The common mistake is charging the whole pack to one meal. A meal that uses 60g from a 1kg bag of rice does not cost the whole bag; it costs the 60g it used. Work in fractions: pack price divided by pack size, multiplied by the amount in the recipe.

That is the calculation that makes bulk buying look sensible, and it is also the one that makes it look less impressive than the shelf label suggests - a larger pack lowers the per-gram price, but only for the portion you eat, not for the portion still in the cupboard.

Then divide by the number of portions the dish actually makes, which is the number you will eat, not the number the recipe claims.

How to Handle the Spoonful Problem

Spices, oil, stock, mustard, soy sauce and vinegar are used in amounts too small to price sensibly and too numerous to ignore. Pricing a teaspoon of paprika to two decimal places is false precision.

The workable convention is a flat allowance - somewhere around ten to twenty pence per portion covers seasoning, oil and sauces for most home cooking. State it as an assumption rather than pretending it is zero, because a costing that excludes the cupboard and one that includes it are different claims even when they land on the same headline figure.

The exception is anything used in quantity. If a recipe takes three tablespoons of olive oil, that is a real cost and should be counted properly.

The Waste Adjustment Nobody Makes

A costing assumes every gram bought gets eaten. In practice the half bag of spinach that goes off is part of what the meal cost, and ignoring it is why real spending exceeds calculated spending so reliably.

The honest version is to cost the pack you had to buy when you cannot use the remainder for anything else. If a recipe needs 50g of an ingredient that only comes in 200g packs and nothing else in the week uses it, that meal effectively cost the whole pack.

This is a strong argument for building a week from a short list of ingredients used repeatedly, which is the actual reason repetitive plans are cheaper - not the shelf prices.

What the Number Is For

Comparison, mostly. A cost per portion is most useful for deciding between two options - this chicken dish against that lentil one - rather than as an absolute claim, because the assumptions behind any single figure are doing a lot of work.

It is also how to test advice. When a plan claims a weekly figure, the question worth asking is whether it counts cupboard staples, whether it assumes every gram is eaten, and how many people it feeds. Most disagreements about whether meal prep is cheap come down to those three, not to the food.