How to Actually Save Money in a Sale (Discount Math Made Simple)
Why '50% off then 20% off' isn't 70% off, how to spot a fake bargain, and the quick math that tells you what you're really paying.
Sales are designed to make you feel like you're winning. Bright "70% OFF!" signs trigger a sense of urgency and reward, which is exactly the point. A little discount math cuts through the psychology and tells you what you're really paying, and whether it's actually a deal.
The basic discount calculation
To find a sale price, multiply the original by (1 − the discount as a decimal):
Sale price = original × (1 − discount/100)
A $80 jacket at 25% off = 80 × 0.75 = $60, saving $20. Simple enough. The confusion starts when discounts stack.
The stacked-discount trap
"Take an extra 20% off already-reduced prices" sounds like it adds to the first discount. It doesn't, the second discount applies to the new, lower price. Watch what happens to a $100 item:
| Offer | Calculation | Final price | Real total discount |
|---|---|---|---|
| 50% off | 100 × 0.50 | $50 | 50% |
| 50% off, then 20% off | 100 × 0.50 × 0.80 | $40 | 60% (not 70%) |
| 30% off, then 30% off | 100 × 0.70 × 0.70 | $49 | 51% (not 60%) |
Each discount acts on whatever price comes before it. 20% off $50 is only $10, not $20. So stacked discounts always total less than the two percentages added together, a gap retailers are happy for you not to notice.
The fake-bargain problem
A huge percentage off means nothing if the "original" price was inflated to begin with. A sofa marked down "60%" from an original nobody ever paid may still cost more than a competitor's everyday price. The discount is marketing; the final price is reality.
That crossed-out "original" price is an anchor, it makes the sale price feel like a steal by comparison. Judge the item by its final price and its value to you, not by how far it has "fallen."
How to shop the math, not the hype
- Calculate the final price and compare it to other sellers, not to the original.
- For stacked offers, multiply the decimals (× 0.50 × 0.80), don't add the percentages.
- Ask "would I buy this at this price if it weren't on sale?" If not, it's not a saving, it's a purchase you didn't need.
- Don't forget tax, in the US it's added on top of the sale price at checkout.
See the real sale price instantly. Enter the original price and discount to get the final price and exactly what you save.
Open the Discount Calculator →The bottom line
Discounts are math dressed up as excitement. Multiply stacked offers instead of adding them, judge deals by the final price rather than the percentage, and never let a crossed-out number talk you into buying something you didn't want. That's how you actually save in a sale.
Frequently asked questions
How do I calculate a discount?
Multiply the original price by the discount percentage and divide by 100 to get the saving, then subtract it. Or multiply the price by (1 − discount as a decimal): for 30% off, multiply by 0.70.
Is 50% off then 20% off the same as 70% off?
No. The second discount applies to the already-reduced price. 50% off then 20% off is a total of 60% off, not 70%. Stacked discounts multiply rather than add.
How can I tell if a sale is a genuine bargain?
Ignore the percentage and look at the final price. Compare it to what the item usually costs elsewhere and to what you'd willingly pay. A large discount off an inflated 'original' price can still be overpriced.