About the Double Discount Calculator
Stores love offers like "30% off, plus an extra 20% off the sale price". It sounds like 50% off, but it is not: the second discount is applied to the already-reduced price. This double discount calculator stacks up to three percentage discounts in order and shows the final price, the saving at each step and the single equivalent discount.
Use it for department store sales, clearance racks with an extra percent off at checkout, loyalty coupons on top of a promotion, or trade discounts in a business quote. Leave the third discount at 0 if you only have two.
The order of percentage discounts does not change the final price, because each one multiplies the price by (1 − rate). Sales tax, if you add it, is charged on the final discounted price.
With the default inputs, the final price (before tax) is $67.20. Change any value above to recalculate instantly.
How to use the double discount calculator
- 1Enter the original tag price.
- 2Enter the first discount (the advertised sale).
- 3Enter the extra discount taken off the sale price, and a third if you have one.
- 4Optionally add sales tax.
- 5Compare the combined discount with the simple sum to see the real deal.
Formula and method
Each stacked discount is taken off the price that is left after the previous one, so the price is multiplied by (1 − rate) once for every discount. Multiplying the factors together gives the single equivalent discount: 30% then 20% is 1 − 0.7 × 0.8 = 44%, not 50%.
Because multiplication is commutative, the order of percentage discounts does not matter. Order only matters when a fixed-dollar coupon is mixed with percentage discounts. Sales tax is charged on the final price.
- P
- Original price
- d₁, d₂, d₃
- Discount rates as decimals (20% = 0.20)
Worked examples
30% off plus an extra 20% off
30% off $120 is $84. The extra 20% comes off $84, saving $16.80 more, so you pay $67.20. That is a combined 44% discount — not the 50% the ad suggests.
Three discounts on $200 with 6% tax
$200 × 0.5 × 0.8 × 0.9 = $72, a 64% combined discount (not 80%). Tax at 6% adds $4.32 for a total of $76.32.
40% off, then 25% off at checkout
$79.99 × 0.60 × 0.75 ≈ $36.00. The two discounts combine to exactly 55% off (1 − 0.6 × 0.75), saving about $43.99.
Frequently asked questions
Is 30% off plus 20% off the same as 50% off?+
No. The extra 20% is taken off the reduced price, so the combined discount is 1 − 0.7 × 0.8 = 44%. On a $100 item you would pay $56, not $50.
Does the order of stacked discounts matter?+
Not for percentage discounts: 20% then 10% gives the same final price as 10% then 20% because the multipliers are the same. Order matters only if a fixed-dollar coupon is mixed in — taking dollars off first leaves a smaller base for the percentage.
How do I calculate an extra percent off a sale price?+
Multiply the sale price by (1 − extra rate). For an extra 15% off a $68 sale price: 68 × 0.85 = $57.80. To work from the original price, multiply by both factors.
What is the formula for successive discounts?+
For two discounts a% and b%, the equivalent single discount is a + b − (a × b ÷ 100). For 30% and 20% that is 30 + 20 − 6 = 44%.
Is sales tax charged on the final price?+
For store discounts, yes — tax is normally charged on the price after all store markdowns and store coupons. Some states tax manufacturer coupons differently.