How to catch shrinkflation using your own receipts

Shrinkflation is a price rise disguised as a packaging decision. The number on the shelf does not move. The contents do.

It works because shoppers remember prices and do not remember weights. Ask someone what they pay for their usual coffee and they will tell you within a krona. Ask how many grams are in the bag and most people genuinely do not know.

What it looks like

Seventeen per cent is not a rounding error, and it is invisible at the shelf because there is nothing to compare against. The old pack is gone. The only record that it was ever 500 grams is on a receipt you probably threw away.

Why you cannot catch it in the shop

Every other kind of price change leaves a trace you can see while standing there. A rise from 59,90 to 64,90 is visible if you were paying attention last week. A promotion is announced. A cheaper competitor is on the same shelf.

A size change leaves no trace at all. The new pack is frequently redesigned at the same time, often to the same height and width with a different depth, so it does not even look smaller. Occasionally the packaging draws attention to a new format in a way that reads as an improvement.

This is the one grocery phenomenon that genuinely requires a purchase history to detect. Everything else is a comparison across products at a moment. This is a comparison of one product across time, and you either wrote the weight down or you did not.

How to detect it yourself

You need three fields per purchase and nothing more: the product, the package size, and the price. Then:

• Work out the unit price for each purchase, price divided by size in a standard unit.
• Sort the purchases of each product by date and look for the size changing.
• Where it changes, compare the unit price before and after. That difference is the real price change, regardless of what the shelf price did.

The trap is step one. Package size lives in the product text, not in its own column, and the text is abbreviated inconsistently. KAFFE 500G and KAFFE MELLANROST 500 G may be the same article in different years. Until you have decided those are the same product, the size change looks like two unrelated items.

What counts as shrinkflation and what does not

Not every size change is a hidden rise. A genuinely new format at a proportionally lower price is just a smaller pack. The test is whether the unit price moved.

A useful threshold is a few per cent. Package weights vary slightly for legitimate reasons, drained weights differ from gross weights, and rounding in the product text loses precision. A 2% change is noise. A 15% change is a decision somebody made.

It is also worth separating shrinkflation from its cousin, where the recipe changes rather than the size, and a cheaper ingredient replaces a more expensive one at a constant price and weight. Receipts cannot see that one at all.

What to do about it

Realistically, nothing that changes the manufacturer’s mind. The value of catching it is that it moves the decision from loyalty to arithmetic.

A product you have bought for years on the assumption that it is good value may have drifted 20% above its competitors while you were not looking, and the only reason you have not switched is that its price tag never changed. Knowing that is the whole benefit. It usually costs the manufacturer one customer and costs you nothing.