The UK Grocery Savings Tracker: Compare Supermarket Offers and Build a Cheaper Basket

Overview

A supermarket offer is only useful if it lowers the cost of the items you actually need. A two-for-one promotion may be poor value if you would normally buy one, while a lower shelf price can become less attractive once a delivery charge, minimum basket or wasted food is included.

This tracker is designed for a regular basket of staple products. It gives you a consistent way to compare supermarkets and decide whether a deal, loyalty price or bulk purchase is worth using. You can apply it to a weekly shop, a monthly household stock-up or a smaller top-up shop.

The basic calculation is:

Total basket cost = item prices + delivery or collection charges - applicable discounts

For a fair comparison, also record the quantity you receive and calculate the unit price. That means comparing products by price per kilogram, litre, 100g, roll, wash or other relevant unit instead of comparing pack prices alone.

Keep your basket practical. Include the products you buy repeatedly, such as bread, milk, eggs, rice, pasta, fruit, vegetables, meat or alternatives, breakfast items, cleaning products and toiletries. A smaller, realistic basket is more useful than a long list of items that changes every week.

How to estimate your cheapest basket

Start by creating a basket template with four columns: product, required quantity, comparable unit and price. Add a fifth column for notes, such as “loyalty price”, “multibuy” or “own-brand alternative”. This lets you distinguish a normal price from a conditional saving.

1. List your essentials. Use the same products and quantities each time. If the household uses two loaves and one large pack of rice in a week, record those quantities rather than choosing whichever pack happens to look cheapest.
2. Record the standard price. Note the shelf or online price before applying a promotion where possible. This makes it easier to see the actual effect of an offer.
3. Record the offer price and conditions. Check whether the discount requires a loyalty account, a minimum quantity, a particular payment method or a minimum spend.
4. Convert to a unit price. Divide the total price by the product quantity. For example, a hypothetical 750g product costing £3 has a unit cost of £4 per kilogram.
5. Add fulfilment costs. Include delivery, collection or travel costs. If you are comparing an online shop with a physical shop, treat the cost of an additional journey as part of the decision, even if you do not assign it an exact cash value.
6. Check substitutions and waste. A cheaper pack is not a saving if part of it will be thrown away. Only count a multibuy as a saving when you expect to use the extra quantity within its usable life.

For each supermarket, add the adjusted price of every item and then add the delivery or collection charge. Compare the completed basket total, not just the subtotal shown beside a promotional banner. You can also calculate the saving against your usual shop:

Percentage saving = (usual basket cost - new basket cost) ÷ usual basket cost × 100

Use the same basket and quantities when repeating the calculation. Otherwise, a lower total may simply reflect buying fewer items.

Inputs and assumptions

Your result is only as useful as the inputs behind it. Decide the following before comparing supermarket offers.

Product specification

Define what counts as a match. “Pasta” could mean a particular shape, a standard pack size or any suitable own-brand version. If you are happy to switch between brands, create two comparisons: a like-for-like branded basket and a flexible basket that allows own-brand alternatives.

Pack size and unit price

Pack sizes vary, so record the quantity as well as the price. A larger pack may have a lower unit price, but only choose it if you have enough storage and will use it before quality declines. For household products, compare meaningful measures such as cost per wash for laundry detergent or cost per roll for toilet paper.

Loyalty pricing

Keep loyalty prices in a separate column. This avoids treating a conditional price as the standard cost and helps you decide whether joining or using a scheme changes your personal basket. Do not assume every loyalty offer is the best option: compare its price with other supermarkets and suitable alternatives.

Multibuys and bulk purchases

Calculate the cost of the full quantity you must buy. If one item costs £2.20 and a three-item offer costs £5, the saving is £1.60 only if all three items would otherwise have been purchased. If you need one item, the relevant comparison may be £2.20 versus £5, not £2.20 versus £1.67.

Delivery, collection and travel

Include any visible charge in the basket total. If a delivery pass or subscription is involved, allocate its cost across the shops you expect to make during the relevant period rather than ignoring it. Keep this as an estimate and label the assumption clearly, because your actual usage may differ.

For broader savings ideas, see our guide to the best UK supermarket offers. If you use several types of saving together, our guide to stacking UK discounts explains how to assess voucher codes, cashback and loyalty points without counting the same saving twice.

Worked examples

The following examples use invented figures to show the method, not current supermarket prices.

Comparing a standard item with a larger pack

Suppose a 500g bag of rice costs £1.50 and a 1kg bag costs £2.40. The smaller bag costs £3 per kilogram. The larger bag costs £2.40 per kilogram, so it has the lower unit price. If your household will use the full kilogram and storage is not a problem, the larger pack is the better value. If half may remain unused, record the likely usable quantity before deciding.

Testing a multibuy

Imagine one bottle of a household cleaner costs £3, while a three-bottle offer costs £7.50. The multibuy reduces the effective price to £2.50 per bottle. It saves £1.50 against buying three separately, but it does not save £2.50 if you only need one bottle. Put the offer in your tracker only when the extra two bottles fit your normal buying pattern.

Adding delivery to the comparison

Assume Supermarket A has a basket subtotal of £42 and a £3 delivery charge. Supermarket B has a subtotal of £44 but free collection that fits an existing journey. Supermarket A’s delivered total is £45, while Supermarket B’s cash total is £44. The cheaper shelf prices at A do not produce the cheaper overall option in this example. If collection requires a separate trip, add an estimated travel cost or mark the result as conditional.

Comparing a loyalty price

Suppose an item is £2.80 at the standard price and £2.30 with a loyalty account. Record £2.30 in the loyalty basket only if you are eligible for and willing to use that scheme. Then compare the same product, or a suitable alternative, elsewhere. The tracker should show both the ordinary and conditional totals so you can see how much of the saving depends on the offer remaining available.

When to recalculate

Revisit your tracker whenever the prices or assumptions behind it change. A practical routine is to check your core basket before a planned shop, then update the full comparison when you notice a meaningful change.

• When staple prices change: update products that make up a large share of your basket first.
• When an offer starts or ends: record the start and end dates if shown, and remove expired promotions from your comparison.
• When pack sizes change: recalculate the unit price rather than relying on the previous result.
• When your household changes: adjust quantities for holidays, guests, dietary changes or a different number of shoppers.
• When delivery arrangements change: review charges, collection plans and any subscription allocation.
• When waste changes: reduce bulk buying if food or household products are regularly left unused.

For a repeatable monthly check, duplicate your basket template and date each version. Keep the previous total beside the new one, then note what changed: price, pack size, promotion, supermarket or quantity. This creates a useful record of your own spending without pretending that one supermarket is always cheapest for every household.

Finish each comparison with three decisions: which items to buy, where to buy them and which offers to ignore. Check the final basket total, unit prices and fulfilment cost before ordering. Then save the updated list for the next shop. That simple habit turns supermarket offers and cheap grocery deals into a measurable plan rather than an impulse purchase.