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.

What is the Discount Stacking Calculator?

Free discount stacking calculator. Apply two or more sequential discounts to a price and see the real final price, total saving and effective percentage off — which is always less than simply adding the percentages. Runs entirely in your browser — nothing is uploaded. It runs free in your browser on Gera Tools, with nothing uploaded.

Discount Stacking Calculator

Name: Discount Stacking Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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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%

Why stacking feels misleading

The gap between “what you expect” and “what you get” widens the more individual discounts you stack. Each successive discount has a smaller base to work on, which is why three 10%-off coupons combine to 27.1% — not 30%. Retailers rely on this effect: advertising “extra 20% off sale prices” sounds enormous, but if the sale price was already 50% off, the combined saving is 60%, not 70%.

When to use this tool

Shoppers: When you have multiple promo codes or a site-wide sale plus a coupon, enter both to see what you will actually pay. The step-by-step breakdown lets you verify each discount applied correctly at checkout.

Retailers and marketers: Before publishing a stacked promotion, run the numbers here to confirm the true margin impact. A “20% + 10%” offer feels generous but only costs 28% off gross — useful for crafting promotions that are both compelling and sustainable.

Finance and purchasing: When comparing supplier quotes that combine different trade discounts and rebate tiers, the effective percentage gives you a single number to rank offers.

Common mistakes to avoid

Do not add percentages together in your head — always multiply the remaining fractions.
The order of percentage-only discounts does not change the final price (multiplication is commutative), but it does change the intermediate prices shown in the breakdown.
If a discount is a fixed-amount voucher rather than a percentage, the order matters and you should subtract the fixed amount first before applying percentage discounts to get the most accurate result.

Everything runs in your browser — nothing is uploaded or stored.