Discount Calculator
Find the sale price and what you save — including the real math behind stacked "extra % off" deals.
The discount formula
Stacked: Price × (1 − d1) × (1 − d2) (not 1 − d1 − d2)
$80 at 25% off: saves $20 → $60.
Stack an extra 10%: 80 × 0.75 × 0.90 = $54, an effective 32.5% off — not 35%.
$150 item: 30% off brings it to $105.00. An additional 15% off brings it to $89.25. Then a flat $10 coupon applies: $89.25 − $10 = $79.25 final price — a total savings of $70.75, or about 47% off, even though no single discount in the stack was close to 47%.
Order matters here: applying the $10 coupon before the percentage discounts instead would leave less for the percentages to work against, resulting in a slightly higher final price.
Deal math worth knowing
Retail promotions are designed to sound bigger than they are. "20% off plus an extra 10%" is 28% off, not 30%. "Buy one get one 50% off" is only 25% off the pair. And a percentage off a marked-up price can still be more than a competitor's everyday price — always compare the final number, not the discount size. Enter a tax rate above to see the true out-the-door price, and use the percentage change calculator to compare two final prices directly.
Stacked discounts vs. what shoppers assume
| Stack | Feels like | Actually is |
|---|---|---|
| 20% off + extra 10% off | 30% off | 28% off |
| 25% off + extra 20% off | 45% off | 40% off |
| 30% off + extra 15% off | 45% off | 40.5% off |
| Buy one get one 50% off | 50% off | 25% off |
The gap between "feels like" and "actually is" grows with the size of the individual discounts, since each successive percentage applies to an already-reduced amount rather than the original price. This is simply how compounding percentage reductions work — the same underlying math as compound interest, just running in the opposite direction.
Common discount mistakes
- Adding stacked percentages instead of multiplying. The single biggest source of "why is my total higher than I expected" — see the table above.
- Tipping or calculating sales tax on the pre-discount price. Both should generally apply to the discounted price actually paid, not the original list price.
- Ignoring exclusions on the "extra X% off" tier. Many stacked promotions exclude clearance or already-marked-down items from the second discount — always check the fine print before assuming a stack applies.
Frequently asked questions
How do I calculate a discount?
Price × discount % = savings; subtract from price. $80 at 25% off saves $20 → $60.
How do stacked discounts work?
They multiply, not add. 20% then 10% = 0.8 × 0.9 = 28% off, not 30%.
What does BOGO 50% really save?
25% across the two items.
Should a dollar coupon be applied before or after a percentage discount?
Apply the percentage discount first when you have a choice — subtracting a flat coupon afterward gives a lower final price than subtracting it first and taking the percentage off the smaller remainder.
Why do stores show a high "original" price next to the sale price?
This is anchor pricing — a higher reference price makes the discount look bigger by comparison, even if few items sold at that original price.
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Note: Educational tool; store promotions may have exclusions and vary by retailer. Last reviewed: September 2026.