Why is stacking 20% then 10% not 30% off?

Each discount applies to the already-reduced price, not the original. 20% off 100 leaves 80, then 10% off 80 leaves 72 — a 28% effective saving, not 30%. Stacked discounts always compound to less than the sum of the percentages.

How do I calculate the effective discount of stacked offers?

Multiply the remaining fractions and subtract from 1. For 20% then 10%, the remaining fractions are 0.8 and 0.9, so 0.8 × 0.9 = 0.72, meaning you pay 72% and save 28%. The tool does this for any number of discounts.

Does the order of discounts matter?

For percentage-only discounts the final price is the same whatever order you apply them, because multiplication is commutative. Order only matters when fixed-amount vouchers are mixed in, which this tool does not model.

Can I stack three or more discounts?

Yes. Add as many percentage discounts as you like, and each is applied in turn to the running price. The step-by-step breakdown shows the price after every discount so you can see how they compound.

What does the effective discount percentage mean?

It is the single discount that would give the same final price as all your stacked discounts combined. It is calculated as the total amount saved divided by the original price, expressed as a percentage.

Is stacking always worse than one big discount?

Stacking gives less than the naive sum of the percentages, but it still saves money — just less than you might expect. A single 30% discount beats stacking 20% then 10% (which equals 28%).

Completely. All calculations run locally in your browser using JavaScript. No prices or percentages are sent to any server, stored or logged.

Discount Stacking Calculator

Discount stacking calculator

Combine two or more discounts on a single price and see the true compounded saving. It is for shoppers comparing coupon stacks and retailers checking what a layered promotion actually costs, because stacked discounts always save less than the sum of the percentages.

How it works

Each discount is applied in sequence to the running price, not to the original. A discount of d% multiplies the price by (1 − d/100), so applying several discounts multiplies all those factors together:

final price = original × (1 − d₁/100) × (1 − d₂/100) × …

The effective discount is then the total saved divided by the original price. Because the factors multiply rather than add, the result is always below the naive sum of the percentages.

Example

Original price £100, with 20% off then 10% off:

After 20%: 100 × 0.80 = £80
After 10%: 80 × 0.90 = £72
Saved: £28 → effective discount 28% (not 30%)

Stacked discounts	Naive sum	True effective
20% + 10%	30%	28%
50% + 20%	70%	60%
10% + 10% + 10%	30%	27.1%

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