1. Learn to read the unit price, not the shelf price
Every supermarket in the US, Canada and the UK is required to show a unit price — per ounce, per 100 g, per litre, per sheet — in small print on the shelf edge label. Almost nobody looks at it, and retailers know that.
The headline price tells you what you spend today. The unit price tells you what you get. These come apart constantly: the bigger box is often not cheaper per unit, the branded item on a multibuy sometimes beats the own-brand single, and the “value” size of cereal can cost more per 100 g than the standard box sitting beside it.
Train yourself on the ten items you buy every single week. Photograph the shelf labels once, work out the best per-unit option for each, and from then on you are choosing from memory rather than recalculating in the aisle. That one-off twenty minutes covers maybe 40 percent of your annual grocery spend.
Loyalty pricing has made this harder in the last few years. Tesco Clubcard prices, Sainsbury’s Nectar prices and the card-only deals now standard at most US chains mean the shelf shows two numbers, and the unit price printed beside them is not always calculated on the one you will actually pay. Work out which figure applies to you before comparing, and treat a card-only price on a product you would not otherwise buy as marketing rather than a saving. It is only a discount if it is on something already on your list.
Watch for two traps. Unit prices are only comparable within the same measure — a pack priced per item beside one priced per 100 g is not a comparison, and you have to do that maths yourself. And drained weight matters for tinned goods: a tin of chickpeas at 400 g total might be 240 g of chickpeas, and the cheaper tin is sometimes the one with less water.