Double Discount Calculator
Retailers love a "20% off, plus an extra 10% at the till" offer because it sounds like 30% off — but it is not. The second discount applies to the already-reduced price, so the two rates multiply rather than add. This calculator shows the real final price and the true effective discount when two markdowns stack.
- Final price
- Total saved
- Price after first discount
- $80.00
- Final price
- $72.00
- Total saved
- $28.00
- Effective discount
- 28.00%
Stacking 20% then 10% gives an effective discount of 28.0%, not 30% — stacked discounts multiply, they do not add.
How it works
Stacked discounts are applied in sequence. The first discount comes off the original price, giving an intermediate price. The second discount then comes off that intermediate price, not the original. Because the second cut is taken from a smaller base, it removes less in absolute terms than it would have from the full price.
Mathematically, each discount multiplies the price by one minus its fraction. A 20% discount multiplies by 0.80; a following 10% discount multiplies by 0.90. Chaining them gives 0.80 × 0.90 = 0.72, so you pay 72% of the original — a 28% effective discount, not 30%.
The order does not matter: 20% then 10% gives the same final price as 10% then 20%, because multiplication is commutative. What matters is that the rates compound. The calculator reports the intermediate price, the final price, the total saved, and the single effective rate that would produce the same result in one step.
price after first = original × (1 − d1 ÷ 100); final = price after first × (1 − d2 ÷ 100). Effective discount = (1 − final ÷ original) × 100. The two rates compound, so the combined discount is always less than d1 + d2.
Worked example
A 100 item with 20% off then an extra 10% off works out as: after the first discount, 100 × 0.80 = 80; after the second, 80 × 0.90 = 72. You save 28 in total, and the effective discount is 28%, not the 30% you might expect from adding 20 and 10.
Things to watch out for
The headline trap is assuming stacked discounts add up: 20% + 10% is not 30%, it is 28%. The gap widens with bigger discounts — 50% then 50% is 75% off, not 100%, and the item is never free. Order never changes the result. If a second discount is applied before tax while the first is after, or one is a fixed amount rather than a percentage, the simple multiply rule no longer holds and you would need to model each step explicitly.
Frequently asked questions
Is "20% off plus an extra 10%" the same as 30% off?+
No. The extra 10% is taken off the already-discounted price, so the discounts multiply rather than add. 20% then 10% gives a 28% effective discount — you pay 72% of the original price, not 70%.
Does the order of the discounts matter?+
No. Applying 20% then 10% gives exactly the same final price as 10% then 20%, because the price is multiplied by the same two factors either way. Order only matters if other rules, like tax or fixed-amount discounts, are mixed in.
How do I find the single equivalent discount?+
Multiply the "keep" fractions and subtract from one. For 20% and 10%: (1 − 0.20) × (1 − 0.10) = 0.72, so the effective discount is 1 − 0.72 = 28%. The calculator shows this as the effective discount.
Can two discounts ever reach 100% off?+
Only if one of them is 100% on its own. Two partial discounts always leave something to pay — 50% then 50% is 75% off, leaving a quarter of the price, because the second cut applies to what remains after the first.
Related calculators
Disclaimer: This calculator is for educational and informational purposes only and provides estimates, not financial advice. Interest rates, taxes, fees, and local rules vary and change over time. Confirm figures with a qualified professional before making any financial decision.
Last reviewed: 2026-06-22