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Discount Calculator

Enter a price and the percentage off to see what you pay and what you save. Stacked discounts multiply rather than add: 20% off then 10% off is a 28% saving, not 30%. Reverse mode finds the original price, so 45 after 25% off was 60. Add a tax rate to see the price at the till.

Runs entirely in your browser

Updated

How to use the Discount Calculator

  1. 1Choose a mode: a single discount, several stacked discounts, or working backwards from a sale price.
  2. 2Enter the price and the percentage off.
  3. 3Read the final price, the amount saved, and the effective discount.
  4. 4Add a tax rate if you want to see the price you actually pay at the till.

How it works

A single discount multiplies the price by one minus the rate. Stacked discounts are the part people get wrong: 20% off then a further 10% off is not 30% off. The second discount applies to the already-reduced price, so the true saving is 28%.

Working backwards divides rather than multiplies. If an item is 45 after 25% off, the original was 45 ÷ 0.75 = 60.

Where tax is involved, order matters in principle but not in arithmetic: applying a discount and then tax gives the same total as tax then discount, because both are multiplications. The tool applies the discount first, which is how most retailers present it.

The formula

sale price = original × (1 − d) stacked = original × (1 − d₁) × (1 − d₂) original = sale ÷ (1 − d)
original
the pre-discount price
d
the discount as a decimal, e.g. 0.25 for 25%
d₁, d₂
successive discounts applied one after another

Worked example

A 120 coat with 30% off, plus an extra 15% member discount

  1. 120 × 0.70 = 84
  2. 84 × 0.85 = 71.40

Result: 71.40 to pay — a saving of 48.60, an effective discount of 40.5%, not 45%.

Tips and common mistakes

  • Multiply stacked discounts, never add them: 20% then 10% off is 28% off, not 30%.
  • Work backwards from a sale price to check the “was” price a shop advertises.
  • Compare price per unit as well as the discount when pack sizes differ.
  • Read “up to 50% off” carefully — only some items carry the largest discount.

Frequently asked questions

Do stacked discounts add together?
No. Each applies to the price after the previous one. 20% then 10% gives a 28% total saving, not 30%.
How do I find the original price from a sale price?
Use the reverse mode. It divides the sale price by one minus the discount — 45 at 25% off means the original was 60.
Should tax be applied before or after the discount?
The total is the same either way, since both are multiplications. Retailers normally discount first and then tax the reduced price.
How do I take 20% off a price?
Multiply by 0.8. A 75 item at 20% off costs 75 × 0.8 = 60.
What is the total discount from two offers combined?
Multiply what each leaves you to pay, then subtract from one. 20% and 10% leave 0.8 × 0.9 = 0.72 of the price, so the combined discount is 28%.
Is “buy one, get one free” the same as 50% off?
Only if you wanted two. Each item then costs half price, but if you only needed one, you are paying full price for it.
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