Why the cheapest product price can cost more at checkout

Compare the amount you will actually pay

Start with the item price plus delivery and any unavoidable charge. Subtract only discounts that apply to your eligible basket and appear before payment. The CMA's price-transparency guidance explains the importance of showing mandatory charges in the total when they can be calculated, including location-dependent delivery once known.

Illustrative example, not live offers: Shop A charges £29.99 plus £4.99 standard delivery, totalling £34.98. Shop B charges £32 delivered. Shop B is £2.98 cheaper for the same item, condition and delivery address. If Shop A does not show delivery until you enter your postcode, its £29.99 item price remains an incomplete comparison, not a £29.99 delivered deal.

Sources: CMA: Clear and accurate price information

A delivery threshold is a new basket decision

Suppose, in another invented example, your £46 basket has £4 delivery and orders of £50 qualify for free delivery. Adding a useful £4 item brings the payment to £50, the same as paying postage on the original basket. Adding an unwanted £6 item brings it to £52: you spend £2 more, despite the free-delivery message.

That calculation changes if you would have bought the extra item elsewhere anyway. Compare the cost of both intended purchases, and check whether all products count towards the threshold. Also check the basket again after applying a voucher: a reduced qualifying subtotal could bring delivery back. The retailer's final basket decides which rule applies.

Check the voucher against this order

A code that exists online may exclude your product, sale items or existing customers. Check the minimum spend, category, expiry and whether it applies to the item subtotal rather than postage. Judge it by the discount actually shown at checkout. An unconfirmed code is something to test, not a saving to deduct in advance.

Using the first example, assume a valid £5 discount applies at Shop A while delivery stays £4.99. Its confirmed total becomes £29.98, beating Shop B's £32 by £2.02. If the code fails, the comparison returns to £34.98 versus £32. Save the confirmed total, rather than relying on the headline '£5 off'.

Show cashback as a possible later outcome

Now assume Shop B offers potential £4 cashback on an eligible purchase. You still pay £32 today. If the purchase tracks, is approved and pays that amount, the eventual cost would be £28. If it is declined, your cost stays £32. That makes Shop B's possible outcome better than Shop A's £29.98 code total, but its pay-today cost remains £2.02 higher.

Quidco warns that codes not supplied by it can interfere with tracking. TopCashback's terms state that cashback payment and estimated payable dates are not guaranteed. Read the provider's specific retailer offer, including eligible categories and how cashback is calculated. A percentage may use a different base from your whole delivered payment; do not automatically apply it to postage or the full basket.

Sources: Quidco: Why cashback did not track · TopCashback: Terms and conditions

Finish the route you chose

Complete your price research before the cashback visit. Follow the selected provider's tracking instructions for that retailer and avoid mixing cashback or voucher extensions that could replace the referral. TopCashback specifically recommends checking retailer terms and clicking through again for each separate order. Keep the confirmation and tracking record so you can investigate a missing reward through the provider.

Tillio can help compare confirmed cost and assumptions, but it does not guarantee a provider's payout. Its cheapest-delivered label needs known delivery for comparable offers across the shops checked. For your final decision, record pay today first, potential later cashback second, and any unresolved eligibility clearly. Choose the route that fits both your budget now and the uncertainty you are willing to accept.

Sources: TopCashback: Why a purchase did not track