How to Compare Supermarket Prices the Smart Way
How it works5 min readBy Luke DurrantUpdated April 2, 2026
Why the shelf price lies to you
The number on the shelf edge is designed to look competitive in isolation, not to help you compare. A larger pack with a higher total price is often cheaper per unit than the small pack sitting next to it, and two stores can advertise the “same” product at different pack sizes so a direct price match is impossible. The only honest comparison is like-for-like: the same product, normalised to a common unit, totalled across everything you actually buy. That is a lot of arithmetic to do in your head in an aisle, which is exactly why most shoppers default to habit instead of evidence.
Compare the basket, not the item
Retailers compete on a handful of visible “known value items” — the products shoppers remember the price of — and quietly make margin elsewhere. A store can be cheapest on milk and bread while being dearer across the thirty other things in your trolley. Deciding where to shop on the strength of two or three famous prices is how you end up paying more overall. The decision that matters is which store is cheapest for your basket, and that answer changes as prices move.
Build a repeatable comparison
Keep a stable list of what you actually buy, compare the whole list across stores at today’s prices, and re-check periodically because prices change week to week. When the comparison is automated you can make a confident, evidence-based choice in seconds instead of guessing.
| Approach | Effort | Reliability |
|---|---|---|
| Glance at a few shelf stickers | Low | Poor — misses pack size and basket total |
| Compare unit prices item by item | High | Good but rarely done in practice |
| Compare the whole basket automatically | Low | Best — totals everything at today’s prices |
Two ways to compare prices
Frequently asked questions
- Is the cheapest supermarket always cheapest?
- No. A store can lead on a few well-known items and be more expensive across a full basket. Always compare the total of what you actually buy.
- What’s the fairest way to compare two products?
- Unit price — price per 100g, per litre, or per item — because it normalises different pack sizes to a common measure.
- How often should I re-compare?
- Grocery prices change frequently, so a basket that was cheapest at one store last month may not be this month. Re-checking weekly or before a big shop is sensible.