How to Calculate Percentage Discount — Formula & Free Calculator

Updated October 2026 · 4 min read

Whether you are shopping a sale, pricing your products, or figuring out how much you actually saved, the discount percentage formula is one of the most useful calculations in everyday life. Here is everything you need to know, including stacked discounts (two discounts applied one after another).

The Discount Formula

Example Calculations

Example 1 — 30% off £120:

• Savings = £120 × 0.30 = £36
• Sale price = £120 − £36 = £84

Example 2 — 20% off $200, then an extra 10% off: (Stacked discount)

• After 20%: $200 × 0.80 = $160
• After extra 10%: $160 × 0.90 = $144
• Total saving = $56 (28% combined, not 30%)

Why Stacked Discounts Are Not Additive

A common mistake: a "20% off + extra 10% off" promotion is not the same as 30% off. The second discount applies to the already-reduced price, not the original. The combined discount is: 1 − (0.80 × 0.90) = 28%.

The MetricPane Discount Calculator handles stacked discounts automatically — enter both percentages and it calculates the real final price and total percentage saved.

Reverse Discount — Finding the Original Price

If you know the sale price and the discount percentage, you can work backwards to find the original price:

Example: an item costs £70 after a 30% discount. Original price = £70 ÷ 0.70 = £100.