Shrinkflation is easy to suspect and hard to prove: a pack gets smaller, the price stays put, and the only trace is a number on the label. I wanted to know how often it shows up in UK supermarket data in a single week, so I compared two weekly snapshots of the online catalogues of Tesco, Sainsbury's, Asda and Aldi, taken on 27 September and 4 October 2026.
What the scan found
About 71,000 products were on sale at the same retailer in both weeks (Tesco 22,574, Sainsbury's 25,369, Asda 19,868, Aldi 3,588). Of those, 29 changed their pack-size text between the two snapshots:
- 6 got smaller while the shelf price held or rose (the shrinkflation pattern);
- 3 got larger;
- 5 were the same pack written differently (175g becoming 0.18kg, for example);
- 15 could not be compared, usually because one week gave a count ("8 pack") and the other a weight, or no size at all.
Of the six, three were confirmed on the retailers' own product pages:
- Asda, Kenco Millicano instant coffee, both jars. The Decaf and the Original (renamed Americano) went from 100g to 90g, and the shelf price from £3.50 to £4.00. Per kilo that is £35.00 to £44.44, up 27%. Asda shows the £4.00 as a Rollback price, with a was-price of £6.92.
- Sainsbury's Cheese & Garlic Stuffed Mushrooms. 200g to 190g at an unchanged £2.10. The site still showed the old unit price (£10.50 per kg) the following week; at 190g it works out at about £11.05.
The other three need a human. In each the product's name changed along with its size: a seasonal chocolate figure whose listed weight fell with its new name although its unit price implied the same weight both weeks, a multipack whose bar count dropped while its unit price suggests the old count was a labelling error, and a sauce jar replaced under the same product id by a different, smaller kit. Those are exactly the cases an automatic scan gets wrong, so they are flagged rather than reported.
Three confirmed cuts in 71,000 products is a footnote, not a trend. It is one week of data; the scan runs again each month.
Method
Each retailer's whole online range is captured once a week into a dataset, one row per product with the shelf price, loyalty price, pack size and unit price as the retailer publishes them. The scan pairs each product with itself in the previous week by the retailer's own product id, and falls back to a shared EAN barcode when the id changed. It reads the pack size into grams, millilitres or a count, and treats a change within the rounding of the shorter form as a rewrite, not a new pack. Unit prices are converted to per kilo or per litre, because one retailer switches between per 100g and per kilo from week to week.
A product is flagged as shrinkflation only when the quantity fell and the shelf price held or rose. Any product whose name changed as well is marked for a hand check, because a new product under an old id is the commonest false alarm. Promotions are kept as they are: a price shown as a Rollback or a loyalty price is reported as such, not removed.
The same weekly snapshots feed a free index, the UK online shelf-price index. The newsletter first reported these finds in the week 41 issue.
Prices are online shelf prices as published by each retailer on the day shown; they are not store-specific. This article is not affiliated with, endorsed by, or partnered with any of the retailers named; their names are used only to describe public product data, and product names, images and descriptions remain the retailers'.
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