How discounts are calculated
A 25% discount on $120: 120 × 0.75 = $90, saving $30. The percentage always applies to the price right before it — which is why stacked discounts don't simply add.
Stacked discounts: why 25% + 20% ≠ 45%
An "extra 20% off" applies to the already-reduced price. $120 at 25% off is $90; another 20% off that is 90 × 0.80 = $72. Total saving: $48, which is 40% — not 45%. The general rule:
Common discount reference table
| Original | 10% off | 20% off | 25% off | 30% off | 50% off |
|---|---|---|---|---|---|
| $10 | $9.00 | $8.00 | $7.50 | $7.00 | $5.00 |
| $25 | $22.50 | $20.00 | $18.75 | $17.50 | $12.50 |
| $50 | $45.00 | $40.00 | $37.50 | $35.00 | $25.00 |
| $75 | $67.50 | $60.00 | $56.25 | $52.50 | $37.50 |
| $100 | $90.00 | $80.00 | $75.00 | $70.00 | $50.00 |
| $150 | $135.00 | $120.00 | $112.50 | $105.00 | $75.00 |
| $200 | $180.00 | $160.00 | $150.00 | $140.00 | $100.00 |
Reverse: finding the original price
Paid $72 after 40% off and want the original? Divide by (1 − 0.40): 72 ÷ 0.60 = $120. Dividing — not adding 40% back — is the step most people miss.
Frequently asked questions
How do I calculate 20% off quickly in my head?
Find 10% by moving the decimal one place, then double it. For $85: 10% is $8.50, so 20% is $17, leaving $68. For odd amounts, round first and adjust.
Do two discounts of 25% and 20% equal 45% off?
No — the second discount applies to the already-reduced price, so together they're 1 − (0.75 × 0.80) = 40% off. Stacked discounts are always slightly less than their sum.
How do I find the original price from a sale price?
Divide the sale price by (1 − discount as a decimal). If something costs $63 after 30% off, the original was 63 ÷ 0.70 = $90.
Is 'up to 70% off' the same as 70% off?
No — 'up to' means 70% is the maximum discount in the sale, often on a small selection. Check the actual price tag and compute the real percentage: (original − sale) ÷ original × 100.
Should tax be applied before or after the discount?
In virtually all jurisdictions, sales tax is charged on the price you actually pay — the discounted price. Store coupons reduce the taxable amount; some manufacturer rebates work differently depending on local rules.