How we compare your whole basket, not just a few prices
Every few weeks, a headline announces the "cheapest supermarket". It's usually based on a basket of a few dozen items chosen by whoever wrote the article — and it usually crowns a different winner than the last headline did. Both can be honest and both can be useless to you, because your shop is not their basket. Your family doesn't buy the thirty items in a survey. You buy your eighty items, in your sizes, with your brands, your allergies, your fussy toddler and your large dog. The cheapest store for a stranger's basket can be the most expensive store for yours.
That's the first reason BasketBadger compares whole baskets: the only comparison that matters is the one run on your actual list.
The loss-leader problem
Supermarkets know which prices people notice. Milk, bread, bananas, eggs, chicken, mince — the items everybody buys every week get priced to within a penny of each other, and sometimes below cost, because they set the shopper's sense of whether a store is "cheap". Economists call them known-value items; the trade calls them traffic builders. Either way, the margin given away on milk comes back somewhere you weren't watching: the sauce jars, the cleaning spray, the bigger pack that's actually worse per kilo.
A comparison built on headline items therefore measures exactly the prices stores have engineered to look identical. The differences that decide what you really pay live in the long tail of your list — and that's why the whole basket, item by item, is the only honest unit of comparison.
The five things a fair comparison has to count
When BasketBadger prices your basket at each store, the total it compares is built from five ingredients. Miss any one of them and the "winner" can flip.
- Every item, matched exactly. The same product, or the honest equivalent — not a smaller pack quietly swapped in. Pack size games are the oldest trick on the shelf, so matching is done at the level of the exact variant where we can, and unit prices are watched where we can't.
- Promotions, actually applied. A shelf full of offers means nothing until you know which ones your basket triggers. Meal deals, multibuys and thresholds have to be simulated against your real quantities — our guide to promotion maths shows how much this moves a total.
- Loyalty prices, counted openly. If a total depends on scanning a Clubcard or a Nectar card, it should say so. Two-price shelves have changed what "the price" even means — we unpack that in loyalty prices explained.
- Missing items, priced in as a penalty. A store that doesn't stock six of your items hasn't saved you money; it has given you a second trip. Our verdicts name the missing items and count the gap against the store, so a partial basket can't win by looking cheap.
- The cost of getting it home. Delivery fees and collection charges belong in the total they belong to. A £3 shelf saving with a £4.50 delivery slot is a £1.50 loss wearing a costume. More in click & collect vs delivery.
Why one store, not a split shop?
The mathematically cheapest answer is often "buy these eleven items here and the rest there". It's also, for most households, a fiction: the second trip costs time, fuel or a bus fare, and a second delivery costs a second fee and a second minimum basket. So our headline verdict is always the cheapest single store for the whole basket. A split is shown only as a footnote, and only when the saving clears a threshold that makes the extra trip genuinely worth it — with the size of the saving stated, so you can decide like an adult.
A small worked example. Two stores price a 42-item weekly basket. Store A wins 26 items, Store B wins 16 — so A "feels" cheaper. But B's wins are concentrated in the expensive lines (meat, coffee, nappies), A's in the cheap ones (pasta, tins, own-brand biscuits). Shelf prices alone: A £71.40, B £69.85. Then the offers run: A has a meal deal your basket completes, saving £3.50 — A drops to £67.90. B has a spend-£70-save-£7 voucher you now miss by 15p. Delivery: A charges £2.99 for your slot, B collects free. Final honest totals: A £70.89, B £69.85 — B wins, by £1.04, for reasons no headline price anywhere revealed. That invisible £1 is what whole-basket comparison exists to find, every week, on your list instead of a survey's.
What we do when we don't know
No comparison covers every store at full depth from day one, and pretending otherwise would break our third promise: we show our working. If a store didn't answer a price check, or our coverage of it is shallow, the app says so next to its total. A comparison that admits its edges is worth more than one that hides them — because the total you're trusting is your money, not our marketing.
See how the verdict is built → · Next guide: meal deals, multibuys and BOGOFs →