A shelf label says “special,” but you cannot remember what the item normally costs. A price book is simply a small record of prices you have actually seen or paid for the groceries you buy repeatedly.
Start with a handful of regular items rather than the whole supermarket. Record the date, shop, product, pack size, price and whether the price depended on a promotion or membership. A notebook or simple spreadsheet is enough.
Keep comparisons genuinely comparable
Use a common unit when quantities differ. For a fictional example, a 500 g pack costing three units is six units per kilogram. A 750 g pack costing four units is about 5.33 per kilogram. The larger pack has the lower unit price, but it is useful only if you will use it and can afford the purchase.
Do not silently compare a concentrated product with a ready-to-use version or a premium item with a different grade. Note the differences that matter to your household. The record should support your choice, not flatten every product into one number.
Give the record a short life
Prices change. Keep dates visible and replace old assumptions with recent observations. A price from six months ago is a historical reference, not evidence that today’s shop is overcharging.
Use receipts you already have and spend a few minutes updating the items that matter most. Avoid travelling to several distant shops to save a small amount without counting the journey’s time and cost.
When a promotion appears, ask three questions: is the unit price lower than recent comparable prices, do I need the item, and can I store and use the quantity? If one answer is no, the offer may not suit you.
The price book’s value is better memory, not perfect prediction. After a few shopping trips, you can recognise a meaningful change and make a calmer decision without relying on the colour of the sale label.