Everyday Money
Discount Stacking Calculator
See the final price when two or three discounts stack one after another.
How stacked discounts work
A 20% off then 10% off is not 30% off — the second cut applies to the already-reduced price. Enter discounts in the order the till or checkout applies them to see the true final price and effective percentage off. Useful for sale-plus-voucher baskets and for checking marketing claims that round the story in the customer’s favour. Mixed percentage and fixed pounds-off codes are especially sensitive to order. After you know the net price, test whether the deal still makes commercial sense with discount profitability or recover the original with reverse discount. General percentage puzzles sit on reverse percentage. Arithmetic only — not a promotions policy. Marketing teams writing site banners should quote the effective percentage when two codes combine, or risk advertising claims that operations cannot honour at the till. Finance should test stacked nets against contribution so a viral double-discount week does not quietly destroy margin. Keep a screenshot of checkout order rules beside the calculator when training junior merchandisers.
Worked example
Item £100. First 20% off → £80. Then 10% off → £72. Effective discount 28%, not 30%. A £10 voucher after the percentages would take £72 to £62 (38% effective off the original). Apply the voucher before percentages and you get a different final — always match checkout order.
Limits and assumptions
Exclusions (‘not valid on sale items’) are not enforced by the maths — read the small print. Loyalty-tier prices and employee discounts may use different bases. Not legal advice on advertising claims.
Frequently asked questions
Why isn’t 20% + 10% equal to 30%?
The second percentage multiplies the reduced price. Combined factor is 0.8 × 0.9 = 0.72, i.e. 28% off.
Does order of discounts matter?
Yes when percentages and fixed pounds mix, or when one code excludes sale items. Match checkout order.
Can I include a fixed pounds-off voucher?
Yes — apply it in the same sequence the till uses, usually after percentage offers.
How do I quote the effective percentage?
Effective % off = 1 − (final ÷ original), shown as a percentage. Use that in margin tests.
What about BOGOF deals?
Convert to an effective price per unit first, then compare with stacked percentage codes on the same basis.