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How to calculate a discount

"30% off" is easy until you're standing in a shop doing it in your head, or a second discount stacks on top. This guide gives you the formula, a mental shortcut, and the one rule people get wrong about stacked discounts.

The fastest way

Enter the price and the percentage into the Discount Calculator and it shows the amount saved and the final price. Read on for the maths.

The formula

Amount off = price × discount%. Sale price = price − amount off. The faster route is to compute what you pay directly: 

25% off $80
pay 75% → 80 × 0.75 = $60

Stacked discounts multiply

This is the trap: 20% off then an extra 10% off is not 30% off. Each discount applies to the running price, so you multiply: 

0.80 × 0.90 = 0.72  →  28% off, not 30%

Working backwards

To find the original price from a sale price, divide by (1 − discount). A $60 item after 25% off was 60 ÷ 0.75 = $80. For any other percentage question, the Percentage Calculator handles it.

Related everyday maths

Splitting a bill and adding gratuity is the same kind of calculation — the Tip Calculator does it in one step.

A note on privacy

The Discount Calculator runs entirely in your browser — nothing you enter is uploaded.

Open the Discount Calculator →

Common questions

How do I calculate a discount?

Multiply the price by the discount percentage to get the amount off, then subtract. A 25% discount on $80 is 80 × 0.25 = $20 off, so the sale price is $60. Or shortcut it: pay (100 − 25)% = 75% of the price, i.e. 80 × 0.75 = $60.

How do stacked discounts work?

Stacked discounts multiply, they don't add. 20% off then an extra 10% off is not 30% off — it's 0.80 × 0.90 = 0.72, so 28% off. The second discount applies to the already-reduced price.

How do I work out the original price from a sale price?

Divide the sale price by (1 − discount). If an item is $60 after 25% off, the original was 60 ÷ 0.75 = $80.

Is any data sent to a server?

No. The calculation runs entirely in your browser — nothing you type is uploaded.