Stacked Discounts Explained: A Shopper's Checklist

To find a sale price, multiply the original price by (1 − discount ÷ 100): 25% off 120 is 120 × 0.75 = 90. When a second discount is applied on top, such as "an extra 10% off sale prices", you multiply again rather than adding the percentages, so 25% plus 10% gives a total of 32.5% off, not 35%. That one rule explains most of the confusion around sales.

Here is how to work out any discount, why stacking behaves the way it does, and a checklist to run before you buy.

How do you calculate a discount?

Two quick formulas:

• Savings = price × discount ÷ 100
• Sale price = price × (1 − discount ÷ 100)

For a 120 jacket at 25% off: savings 30, sale price 90.

Why don't stacked discounts add up?

The second discount applies to the already-reduced price, not to the original. Take the same 120 jacket:

1. 25% off 120 → 90
2. An extra 10% off 90 → 9 off → 81

You save 39 in total, which is 39 ÷ 120 = 32.5% of the original price. If the discounts added up, you would pay 78 (35% off). The difference is small here, but it grows as the percentages grow.

The extreme case makes the point: 50% off, then an extra 50% off, does not make an item free. An 80 item drops to 40, then to 20: a total of 75% off.

The general formula for two discounts a and b is:

Effective discount = 1 − (1 − a) × (1 − b)

For 30% and 15%: 1 − 0.70 × 0.85 = 0.405, or 40.5% off. Order doesn't matter; 10% then 25% gives exactly the same price as 25% then 10%.

A sale shopping checklist

Before you decide a deal is a deal, run through these:

1. Check the original price. A discount off an inflated "was" price is not a saving. If you can, compare against what the item sold for a few weeks ago.
2. Calculate the effective discount for stacked offers. "30% off + extra 15%" on a 249.99 item is 148.74, saving 101.25, an effective 40.5%, not 45%.
3. Compare unit prices, not just percentages. "Buy one, get the second half price" is 25% off when you buy two, and no discount at all if you only needed one.
4. Factor in shipping and returns. A cheaper item with a 9.99 shipping fee and no free returns may cost more than a smaller discount elsewhere.
5. Know whether tax is added after the discount. In most places, sales tax or VAT is charged on the discounted price. The VAT Calculator can add it back if a price is shown without tax.
6. Check the cap. Some promo codes give "20% off up to 50", so the percentage stops applying after a certain basket size.

How to use the Discount Calculator

The Discount Calculator handles single and stacked discounts:

1. Enter the Original price.
2. Enter the Discount percentage.
3. If there is a second discount applied after the first, enter it in Extra discount (optional). Leave it at 0 otherwise.
4. Read the Final price, how much You save, and the Effective discount as a single percentage.

Discounts must be between 0 and 100%. Results are rounded to the cent, and everything updates in your browser as you type.

Working backward: what was the original price?

If you know the sale price and the discount, divide instead of multiplying:

Original price = sale price ÷ (1 − discount ÷ 100)

A shirt on sale for 75 at 25% off originally cost 75 ÷ 0.75 = 100. Subtracting 25% from 75 (to get 56.25) is a common mistake, because the 25% was taken from the original price, not the sale price.

When percentage-off is the wrong comparison

Percentages help compare offers on the same item. They are less helpful across different items or stores. A 10% discount on something you were going to buy anyway saves real money; a 60% discount on something you didn't need costs you 40% of its price. For questions like "what percentage cheaper is store A than store B?", use the Percentage Calculator in percentage-change mode.

FAQ

Is "40% off" the same as "pay 60%"?

Yes. A 40% discount means you pay 60% of the original price. Thinking of it as "pay 60%" makes the final price quicker to estimate: 60% of 150 is 90.

Does the calculator support three discounts?

It takes two: a main discount and one extra discount. For a third, run the final price from the first calculation back in as the new original price.

Why does the effective discount show decimals?

Because combined discounts rarely land on whole numbers. 25% followed by 10% is exactly 32.5%, and the calculator shows it that way rather than rounding it.

Check what you will actually pay with the Discount Calculator.