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Why 20% off plus 10% off does not make 30% off

An offer of “20% off, plus an extra 10% at checkout” sounds like 30%, but it is not. The difference matters to you as a seller when you design the offer, and to your customer when they compare two deals.

Published · 2 min read

The second discount applies to the reduced price

With two discounts in a row, the first applies to the original price and the second applies to the price after the first, not to the original. So the second discount is smaller than its number suggests.

Worked example

Original price 100, 20% off and then 10% off.

After the first discount: 100 − 20 = 80.

The second discount is 10% of 80, which is 8, so the price becomes 72.

The real total discount is 28%, not 30%.

The general rule: final price = price × (1 − first discount) × (1 − second discount). That is also why the order does not matter. 10% then 20% gives exactly the same result.

Comparing two offers on a price of 250

Worked example

20% then 10%: final price 180, a saving of 70.

A single 30%: final price 175, a saving of 75.

That is a difference of 5 per item. It sounds small, but across a campaign of 500 orders it comes to 2,500, and a customer who compares carefully will notice.

How to do it

  1. Open the Discount calculator and type the original price.
  2. Type the first discount rate.
  3. Add an extra discount if there is one. The tool allows several in a row.
  4. You see the saving, the final price and the real combined discount, with the simple sum of the rates for comparison.
Worked example

A single simple discount: a price of 200 with 15% off becomes 170, a saving of 30.

Before you announce the offer

  • Check your margin after the discount, not before. A 28% discount on a product with a 30% margin leaves very little profit. Check the new price in the Profit margin calculator.
  • Word the offer honestly. Saying “up to 30% off” for two stacked discounts can be read as something it is not.
  • If you want to keep a set margin after discounting, work out the right original price from the start with the Selling-price calculator.

Common questions

Can a discount go above 100%?

No. The tool refuses any rate outside 0 to 100 and never gives you a negative price.

Why is the “sum of rates” shown separately?

For comparison only, so you can see the gap between the wrong simple sum and the real discount.

Are the numbers saved?

No, the calculation runs in your browser.