Millions of shoppers could be missing out on potential savings because of hidden codes on supermarket labels that reveal important information about product dates and promotions. While many of us focus on loyalty deals, yellow stickers, or obvious discounts, there are subtle markings on products that can help you shop smarter and make your money go further.

Consumer group Which? recently shared a video on social media, saying: “These are the secret codes supermarkets just don’t want you to know about.” In recent years, some supermarkets have removed visible best-before dates from pre-packaged produce to reduce waste. Instead, they use coded letters and numbers.

In the recent video, a Which? spokesperson explains how to decode the best before dates at some of the biggest UK supermarkets. 

At Asda and Tesco, the codes typically feature a letter and a number. The letters from A to L correspond to the months of the year, while the number indicates the day. For example, a bag of potatoes marked with ‘B12’ would be best before February 12th.

Sainsbury’s uses a different approach. Codes start and end with J and S which stands for the name of the retailer. What you therefore need to look at are the numbers in the middle. The numbers in the middle reveal the day and month so a code like J0910S would indicate that the product is best before October 9.

Marks & Spencer also relies on a combination of letters and numbers to indicate dates. Morrisons’ date system is pretty simple as they just use the letter of the month followed by the date. A pack of leeks shown in the video is labelled ” F10″ meaning February 10. 

Aldi’s system is a bit more complex, using four numbers where the first two show the week of the year and the last two the day within that week, Which? explains in the video. The consumer group advised comparing products side by side when choosing, noting that the item placed on top is more likely to have an extra day of shelf life.

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Promotional deals at supermarkets also carry hidden clues that can help shoppers plan their purchases. At Tesco, for example, small sequences of numbers printed in the fine print of shelf labels reveal when an offer will end. These numbers are often written backwards, so a code like 260225 indicates that the deal expires on February 25.

Sainsbury’s uses a slightly different approach. Instead of showing the end date, the small print displays when the promotion began. Shoppers can then estimate how long the offer will last, it’s typically about two weeks, with many deals ending on a Tuesday.

Aldi also has a system for products nearing the end of their availability. Items about to be discontinued often feature a capital letter D in the corner of the price tag, Sky News reported. 

Reena Sewraz, retail editor at Which?, also told Money: “Supermarket shopping is already a juggling act of budgets, unit prices, and loyalty schemes, making the task of deciphering ‘secret shelf codes’- which show a deal’s true end date – feel like unnecessary effort.

“However, shoppers who know when a promotion expires can make savings if they know when to stock up strategically or hold off – removing the pressure to panic-buy an item they might not need yet.”