Why 20% off followed by 10% off is not 30% off
Successive discounts apply to an already-reduced price. Adding the percentages exaggerates the saving because the second discount uses a different base.
Discount calculator →Multiply the proportions that remain
A 20% discount leaves 80% of the original price. A further 10% discount leaves 90% of that reduced amount. The combined retained proportion is 0.8 × 0.9 = 0.72, giving an effective discount of 28%. In the calculator, enter the percentage removed, not the percentage retained. This distinction is especially important when translating discount conventions between languages.
Check one purchase from start to finish
An original price of 250 becomes 200 after 20% off, then 180 after a further 10% reduction. Total saving is 70, and 70/250 = 28%. Treating the promotion as 30% off would produce 175 and understate the amount payable by 5. Run the calculator twice, using the first discounted price as the second input, to reproduce the correct sequence.
Confirm that the offers can actually be combined
Promotions may have product exclusions, spending thresholds, maximum savings or fixed-value coupons. Read those conditions before applying a mathematical stack. Tax, shipping and membership costs are outside the example. A discount on a second item is also not automatically a discount on the entire basket. The arithmetic explains a permitted sequence, not whether a retailer’s terms allow it.
Try the calculators
- Discount calculator
Find the sale price and how much you save.
- Percentage change
Measure the change between two values.
- Sales tax / VAT / GST
Add tax or extract it from an inclusive price.