What does a dinner actually cost? Work it out per serving.

Budget meal advice usually quotes a national average that does not match your store. This page does the arithmetic on your prices instead. Type what you paid, how big the package was and how much the recipe used, and you get the cost of the recipe and of one serving.

How the calculation works

Cost in recipe = package price × (amount used ÷ package size). A 2 lb bag of rice that cost you $3.20, of which the recipe uses 8 oz, contributes $3.20 × (8 ÷ 32) = $0.80. Add every row for the recipe total, divide by servings for the per-serving figure. That is the whole method; the calculator just saves the division.

Three things that make the number honest

• Use your prices. Prices vary by store, region, brand and week, so a figure copied from a website is a guess about someone else's shopping. Keep the last receipt or check the shelf label; the price per unit printed there is the same ratio this page uses.
• Count the seasoning. Oil, salt, spices and stock cubes are small per recipe, but they are not zero and they are the rows people skip. Enter the jar price and the pinch you used; a quarter teaspoon out of a 2 oz jar is a real, tiny number.
• Round up. Waste, the bit of onion you threw away, the pasta water you salted. If a serving comes out at $1.84, call it $2. Estimates made at the kitchen table skew low.

Where the money usually is

Run three of your regular dinners through the calculator and sort the rows by cost. In most home cooking the protein row is the biggest single line and the vegetables and grains are cheap per serving. That is why budget planning tends to mean stretching the protein (a roast chicken over three dinners), not cutting the vegetables, and why batch cooking lowers cost mainly by using whole packages instead of half of them.

Turning it into a weekly plan

1. Price five dinners you already make. Write the per-serving figure next to each on the weekly planner.
2. Decide the week's number: dinners × people × the per-serving figure you are aiming for.
3. Swap the most expensive dinner for one that reuses an ingredient already on the list, and re-run the sums.
4. Shop from the list only, in aisle order, and keep the receipt for next week's prices.

What to do with the per-serving figure

Two comparisons are worth making once you have it. First, against the same dish bought ready-made or delivered: the gap is usually the clearest argument for cooking the dinner at home, and it is your number, not a claim from a website. Second, against your other dinners: if one recipe costs three times the others per serving, it is a weekend dish, not a Tuesday dish, and the planner should treat it that way. Neither comparison needs to be exact. Within a few cents is plenty for a decision about what to cook.

Common mistakes in the arithmetic

• Mixing units in a row. A 1 lb package with 6 oz used has to be entered as 16 and 6, or 1 and 0.375. The calculator does not convert; it only divides.
• Charging the whole package to one recipe. If you bought a 2 lb bag of rice and used a quarter of it, the recipe pays for a quarter. The rest is next week's dinner, and pricing it twice makes every dish look dearer than it is.
• Forgetting the serving count changes. Doubling a recipe usually doubles the ingredient rows and the servings, so the per-serving figure barely moves; what changes is the shopping bill for the week. Keep both numbers in view.

General information about home cooking costs, not financial advice. Prices differ by store and change weekly; always use your own.