How this calculator works
Enter the original price and a discount percentage to see the sale price and how much you save. Add a second discount only when a store or coupon explicitly stacks a further percentage on top of the first — the field defaults to 0%, which reduces the calculator to a plain single discount.
Stacked discounts do not add together. A sign reading '20% off, plus an extra 10% at checkout' is not offering 30% off — the second discount is taken from the already-reduced price, so the true saving is 28%. This calculator applies the discounts in the correct order so the sale price always matches what a cash register would charge.
The formula
Sale price = price × (1 − discount1 ÷ 100) × (1 − discount2 ÷ 100)Effective discount % = (price − sale price) ÷ price × 100With discount2 left at its default of 0%, the formula reduces to a single discount. When both are set, discount2 applies to the already-discounted price from discount1, not the original price — this is why two stacked percentages never simply add together.
Worked example: 20% off, then an extra 10%
- Start with a $100 item.
- After 20% off: 100 × 0.80 = $80.
- After an extra 10% off that $80: 80 × 0.90 = $72.
- Total saved: $100 − $72 = $28, an effective discount of 28% — not 20% + 10% = 30%.
Frequently asked questions
Why doesn't 20% off plus 10% off equal 30% off?
Because the second discount is calculated on the price after the first discount, which is smaller than the original price. Losing 10% of $80 is $8, not 10% of $100 ($10), so the combined saving is 28%, always a little less than the sum of the two percentages.
In what order are the two discounts applied?
The first discount field is applied to the original price, and the second, if set, is applied to that result. Applying the two discounts in either order gives the same final sale price, since multiplying by two factors is commutative — this calculator shows discount1 first to match how stores typically describe a stacked deal.
Do I need to fill in the second discount field if my sale only has one discount?
No — leave the second discount at its default of 0%. With discount2 at 0%, the formula reduces to price × (1 − discount1 ÷ 100), the standard single-discount calculation.
Can the effective discount ever be negative?
Not with two genuine discounts, since each factor (1 − discount/100) stays between 0 and 1 for valid percentages between 0 and 100. A coupon that increases the price is a surcharge, not a discount, and isn't handled by this calculator.
Does this work for percentage-off coupon codes at checkout?
Yes, as long as the codes apply one after another to the running price, which is how most e-commerce carts stack a storewide sale with a separate promo code. If a coupon instead applies to the original price regardless of other discounts, treat that one as discount1 and put the storewide sale in discount2.