Formula
Price after discount = price × (1 − d ÷ 100)Two discounts: price × (1 − d₁/100) × (1 − d₂/100)Discount % = (original − sale) ÷ original × 100
- d — discount percentage
- Tax is added to the discounted price.
A second discount is taken off the already-reduced price, not the original.
Worked examples
20% then 10% off 1,000
- What do you want to find?
- Price after discount
- Original price
- 1,000
- Discount
- 20 %
- Extra discount
- 10 %
Price after discount
720.00
You save: 280.00
Effective discount: 28%
From 1,000 to 800
- What do you want to find?
- Discount % from original and sale price
- Original price
- 1,000
- Sale price
- 800
Discount
20%
You save: 200.00
How it works
20% off 1,000 leaves 800 and saves 200. Stack a further 10% off and the second discount applies to 800, not 1,000: 800 × 0.9 = 720, an effective discount of 28% — not 30%.
If tax is added it is charged on the discounted price, which is how most shops and online stores calculate it: with 20% off 1,000 and 18% tax you pay 800 + 144 = 944, not 1,000 less 20% plus 18% of 1,000. Work in this order — discount first, tax last — and compare shops on the final figure rather than the headline percentage.
The second mode runs the sum backwards: a price that falls from 1,000 to 800 is a 20% discount. To strip tax out of a final price use GST Calculator. For the change between two prices in either direction see Percentage Change Calculator.
Assumptions and limits
- Discounts above 100% are rejected.
- Tax, if entered, is applied after all discounts.