A fixed-value coupon is not automatically better than a percentage discount. This guide shows how to compare £5-off, £10-off and percentage promo codes against your actual basket, including minimum spends, excluded products, delivery charges and discount caps.
Overview
The best coupon for your order is the one that produces the lowest final cost without encouraging you to buy items you do not need. A £5-off code can be valuable on a modest basket, while a percentage code usually becomes more competitive as the eligible spend increases. However, the headline discount is only one part of the calculation.
Before choosing between coupon codes, check four things:
- Eligible basket value: which products are included in the promotion?
- Minimum spend: must your order reach a threshold before the code applies?
- Discount limits: is there a maximum saving or a per-order cap?
- Final checkout cost: how do delivery fees, surcharges and any changed eligibility affect the total?
For example, 10% off a £40 eligible basket saves £4, so a £5-off code would be better if both codes can be used. On a £60 eligible basket, 10% saves £6 and overtakes the £5 coupon. The crossover point is easy to find: divide the fixed discount by the percentage expressed as a decimal. For a £5 coupon and a 10% coupon, £5 ÷ 0.10 = £50.
This comparison should be made against the eligible subtotal, not necessarily the amount shown in your basket. If a code excludes sale items, gift cards, delivery or a particular category, remove those items from the calculation first.
How to estimate the best coupon
Use this repeatable process whenever you have several working promo codes to compare.
- Record the item subtotal. Add the prices of the products you intend to buy before applying a coupon.
- Remove excluded products. Separate sale items, clearance lines, gift cards, subscriptions or other products that the terms do not include.
- Calculate the eligible subtotal. This is the amount to which the percentage discount or fixed saving can actually apply.
- Test the minimum spend. Confirm whether the eligible subtotal, the pre-discount subtotal or another amount is used to qualify for the code. If the terms are unclear, treat the threshold as a condition to verify at checkout.
- Calculate each discount. For a percentage code, multiply the eligible subtotal by the percentage. For a fixed-value code, subtract the stated amount, subject to any restrictions.
- Apply any cap. If a 20% offer is capped at £10, the saving cannot exceed £10 even when the percentage calculation is higher.
- Add delivery and unavoidable charges. Compare the final payable total, not just the product total.
- Check code usability. A mathematically stronger offer is not useful if it has expired, is limited to new customers, requires a particular payment method or cannot be combined with another offer.
The basic formulas are:
- Percentage saving: eligible subtotal × discount rate.
- Final product total: eligible and non-eligible items combined − valid coupon saving.
- Final checkout total: final product total + delivery and other applicable charges.
For a broader comparison that includes delivery fees, you can also use the discount shopping savings calculator. It is especially useful when a free-delivery threshold changes which coupon gives the lowest overall cost.
Inputs and assumptions
A reliable coupon comparison depends on using the same assumptions for every code. Start with the basket you would buy without a promotion. Do not add unnecessary products simply to unlock a discount unless the additional item is genuinely useful and its cost is included in the final comparison.
Minimum-spend thresholds
A £5-off-£25 code may appear stronger than a percentage offer, but it is only relevant if the eligible basket reaches £25. If your basket is £23, adding a £2 item to unlock the code may be sensible only if you would have bought that item anyway. Otherwise, the extra purchase reduces the real value of the promotion.
Excluded items
Retailer terms may treat full-price, sale and clearance products differently. A basket worth £50 can have a much smaller eligible subtotal if £20 of it is excluded. Read the code conditions before doing the maths; the guide to coupon terms and conditions covers expiry dates, exclusions and minimum spends in more detail.
Discount caps
Percentage codes need a cap check. A 15% discount on £100 is £15, but if the maximum saving is £10, the usable saving is £10. Fixed-value codes normally have a clearer upper limit, although they may also exclude certain categories or require a higher minimum spend.
Delivery and order changes
Compare the full amount payable. A coupon may reduce the item total without changing delivery, or using it may leave the order below a free-delivery threshold. If a code changes the delivery charge, include that difference in the saving rather than comparing the coupon values alone.
Worked examples
The following examples use simple assumptions to show the method. They are illustrations, not current retailer offers.
| Eligible basket | £5 off | £10 off | 10% off | Best discount |
|---|---|---|---|---|
| £30 | £5 | £10 if threshold is met | £3 | £10 off |
| £50 | £5 | £10 if threshold is met | £5 | £10 off |
| £80 | £5 | £10 if threshold is met | £8 | £10 off |
| £120 | £5 | £10 if threshold is met | £12 | 10% off |
In this simplified table, the £10 coupon remains stronger than 10% until the eligible basket passes £100. The £5 coupon and 10% coupon are equal at £50; below that point, £5 off is stronger, and above it, 10% off is stronger. If the 10% offer has a £10 maximum saving, it becomes no better than £10 off once the basket reaches the cap.
Now consider exclusions. Suppose the displayed basket is £80, but £30 of products are excluded. The eligible subtotal is £50. The 10% code saves £5, not £8. A £5 coupon would tie it, while a £10 coupon could be better if its conditions allow the remaining products and its minimum spend is satisfied.
Finally, consider delivery. If the basket is close to a free-delivery threshold, a coupon that lowers the qualifying subtotal may create a delivery charge. A £10 discount could therefore produce a smaller overall saving than expected. Always compare the final checkout totals for each valid code.
When to recalculate
Recalculate your comparison whenever the basket changes, a coupon is replaced, or the retailer updates its terms. The result can change when you add or remove an item, swap a full-price product for a sale item, cross a minimum-spend threshold or reach a percentage discount cap.
It is also worth checking again before seasonal shopping periods, flash sales and larger planned purchases. Promotions may change their eligibility, expiry dates or delivery conditions, and a code that was best for a small order may not be best for a larger one. Treat coupon pages and sale alerts as starting points, then verify the terms displayed by the retailer before payment.
Use this final checklist:
- What is my eligible subtotal?
- Does each code meet its minimum spend?
- What is the exact saving after any cap?
- Are sale items or other products excluded?
- Will delivery or another charge change?
- Is the code valid for my account and payment method?
- Which option gives the lowest final total without extra unwanted spending?
For more practical budget shopping guidance, see how to stack coupons, cashback and loyalty rewards without overpaying, and learn how to distinguish genuine offers from misleading claims in this guide to fake discount codes and sale prices. The strongest coupon is not always the one with the biggest headline number; it is the one that works on your actual basket and leaves you paying less overall.
