To find a discount percentage, subtract the sale price from the original price, divide that saving by the original price, and multiply by 100. For example, an item reduced from $80 to $56 saves $24, and $24 ÷ $80 × 100 = 30%, so the discount is 30%.
That one formula covers almost every sale you will meet in a shop or online: a percentage-off label, a clearance sticker, or a price that has simply dropped. Once you know it, you can check in seconds whether a "big sale" is really as good as it sounds, compare two offers on different items, and work out the final price before you reach the checkout.
The Discount Formula
There are two closely related calculations, and it helps to keep them separate. The first finds how much you save as a percentage. The second finds the price you actually pay.
Discount percentage = (Original price − Sale price) ÷ Original price × 100
Sale price = Original price × (1 − Discount percentage ÷ 100)
The key detail is the denominator: you always divide by the original price, never by the sale price. Dividing by the sale price is the most common mistake, and it inflates the answer. On an $80 item reduced to $56, dividing $24 by $56 gives 42.9%, which is wrong — the true discount is 30% off the original $80.
If you would rather start from the percentage on the label, the second formula does the job. A 25% discount on a $120 jacket means you pay 75% of the price: $120 × 0.75 = $90. Your saving is the other $30.
Worked Examples With Real Numbers
Let us walk through the kinds of discounts you meet most often.
Example 1: 30% off $80
Original price: $80. Sale price: $56. Saving: $80 − $56 = $24. Discount percentage: $24 ÷ $80 × 100 = 30%. Going the other way, 30% off $80 is $80 × 0.30 = $24 off, so you pay $80 − $24 = $56. Both directions agree, which is a useful cross-check.
Example 2: A $45 item reduced to $36
Saving: $45 − $36 = $9. Discount percentage: $9 ÷ $45 × 100 = 20%. This is a tidy, common sale size — one fifth off. If you only knew the sale price and the 20% label, you could recover the original price by dividing: $36 ÷ 0.80 = $45.
Example 3: A $250 television reduced to $187.50
Saving: $250 − $187.50 = $62.50. Discount percentage: $62.50 ÷ $250 × 100 = 25%. Larger items make the same percentage feel much bigger in cash terms: 25% off a television saves $62.50, while 25% off a $12 book saves just $3. The percentage is identical; the cash saving is not, which is why retailers love advertising percentages on expensive goods.
Example 4: Finding the sale price from the label
A pair of shoes costs $95 with 40% off. Discount amount: $95 × 0.40 = $38. Sale price: $95 − $38 = $57. Or, in one step: $95 × 0.60 = $57, because you pay the remaining 60%.
| Original price | Sale price | You save | Discount |
|---|---|---|---|
| $80 | $56 | $24 | 30% |
| $45 | $36 | $9 | 20% |
| $250 | $187.50 | $62.50 | 25% |
| $95 | $57 | $38 | 40% |
| $200 | $150 | $50 | 25% |
The Stacked Discounts Trap
Here is where even careful shoppers get caught. Two discounts applied one after another do not add up. A "20% off, then an extra 10% off" sale is not 30% off.
Take a $100 item. The first discount takes 20% off: $100 − $20 = $80. The second discount takes 10% off the new price of $80, not the original $100: 10% of $80 is $8, so you pay $72. Your total saving is $28, which is a 28% discount — not 30%.
The same logic applies in the other direction. A price that rises 20% and then falls 20% does not return to where it started: $100 becomes $120, then 20% off $120 is $96. Percentages always act on the current price, so order and base matter every time.
When a store offers "an extra 10% off sale items," apply the extra discount to the sale price you see on the tag, and you will get the true checkout price. If you want to check the combined saving as a single percentage, use the formula above on the original and final prices: ($100 − $72) ÷ $100 × 100 = 28%.
The Quick 10% Mental-Math Trick
You rarely need a calculator for a sale if you can find 10% in your head. Ten percent of any price is just that price with the decimal point moved one place left: 10% of $80 is $8, 10% of $46 is $4.60, 10% of $125 is $12.50.
From there, build any common discount by adding or subtracting blocks of 10% and 5%:
- 20% = 10% + 10%. On $80: $8 + $8 = $16 off, so you pay $64.
- 30% = 10% × 3. On $80: $8 × 3 = $24 off, so you pay $56.
- 15% = 10% + 5% (and 5% is half of 10%). On $80: $8 + $4 = $12 off, so you pay $68.
- 25% = 10% + 10% + 5%. On $80: $8 + $8 + $4 = $20 off, so you pay $60.
- 50% = half the price. On $80: $40 off, so you pay $40.
For awkward percentages, round first and adjust. A 33% discount on $90 is roughly a third off: $90 ÷ 3 = $30, so you pay about $60. The exact figure is $90 × 0.33 = $29.70 off, giving $60.30 — close enough to judge the deal in the aisle, and exact enough to spot a mislabelled tag.
Discounts, Taxes, and the Price You Actually Pay
One more distinction matters at the checkout: the discount is usually applied before sales tax, so tax is charged on the reduced price. A $80 item at 30% off costs $56 before tax. With 8% sales tax, you pay $56 × 1.08 = $60.48, not $80 × 1.08 minus $24. If you are comparing an online price that includes tax with an in-store price that does not, compare the pre-tax prices first, then add tax to both.
Also watch for "was/now" pricing where the "was" price was never the normal selling price for long. The formula still tells you the percentage off the stated original price — it just cannot tell you whether that original price was genuine. If the same item is $56 everywhere else, the real saving versus the market is zero, whatever the label claims.
How to Compare Two Deals Quickly
When two offers differ in both price and percentage, convert both to the final price and compare that, not the headline percentage. A 40% discount on a $60 item leaves you paying $36, while a 25% discount on a $40 item leaves you paying $30 — the smaller percentage is the cheaper buy. Likewise, "buy one, get one half price" on two $50 items means you pay $75 for $100 of goods, a 25% discount overall, which may beat a straight 20% off but lose to a 30% off deal.
If mental arithmetic is not your favourite pastime, skip it: our free Discount Calculator works out the discount percentage, the amount saved, and the final price from any two numbers you enter, including stacked discounts.
Frequently Asked Questions
How do I calculate a discount percentage?
Subtract the sale price from the original price, divide the result by the original price, and multiply by 100. For example, ($80 − $56) ÷ $80 × 100 = 30%, so an item reduced from $80 to $56 is 30% off.
Why is 20% off plus 10% off not 30% off?
Because the second discount applies to the already-reduced price, not the original price. On a $100 item, 20% off leaves $80, then 10% off $80 leaves $72, which is a total saving of $28 or 28%, not 30%.
How do I find the sale price when I know the discount percentage?
Multiply the original price by the percentage you still pay. For 30% off a $80 item, you pay 70%, so $80 × 0.70 = $56. Alternatively, work out the discount amount ($80 × 0.30 = $24) and subtract it from the original price.
What is the quickest way to work out a discount in my head?
Find 10% by moving the decimal point one place left, then build the discount from blocks of 10% and 5%. For 30% off $80, 10% is $8, so 30% is $24 off and you pay $56.
Try it yourself: use our free Discount Calculator to get your number in seconds — no sign-up needed.