The Quick Answer
To calculate a discount, multiply the original price by the discount percentage as a decimal to find your savings, then subtract it from the original price. Or do it in one step:
Sale price = Original × (1 − discount ÷ 100)
For example, 25% off an $80 item: $80 × (1 − 0.25) = $80 × 0.75 = $60. You save $20.
If you’d rather skip the math, the discount calculator gives you the sale price and savings instantly. But the shortcuts below are easy enough to do in your head at the store.
The Discount Formulas
There are two numbers people usually want — the savings and the final sale price:
Savings = Original × (discount ÷ 100)
Sale price = Original − Savings, or in one step, Original × (1 − discount ÷ 100)
The two are just different views of the same calculation. If something is 30% off, you’re saving 30% and paying the remaining 70%.
Worked Examples
Example 1 — 25% off $80:
Savings = $80 × 0.25 = $20
Sale price = $80 − $20 = $60Example 2 — 30% off $50:
Savings = $50 × 0.30 = $15
Sale price = $50 − $15 = $35Mental-Math Shortcuts
You can estimate most discounts without a calculator. The trick is to anchor on 10%, which is just moving the decimal point one place to the left.
| Discount | Quick method | Example on $60 |
|---|---|---|
| 10% | Move the decimal one place left | $6 off → $54 |
| 20% | Find 10%, then double it | $12 off → $48 |
| 25% | Divide the price by 4 | $15 off → $45 |
| 50% | Halve the price | $30 off → $30 |
So for 20% off $45: 10% is $4.50, double it to $9, and the sale price is $36. For 25% off $48: divide by 4 to get $12 off, leaving $36.
The 10% anchor works for any discount. Need 30%? Find 10% and triple it. Need 15%? Find 10%, then add half of that (another 5%). Once you can find 10% instantly, every other percentage is one quick step away.
Stacked Discounts Multiply — They Don’t Add
This is the mistake almost everyone makes. When you apply two discounts one after the other, they multiply, not add.
Take “25% off, then an extra 20% off.” It’s tempting to think that’s 45% off — but it isn’t:
Start at 100%
After 25% off: 100% × 0.75 = 75% of original
After 20% off: 75% × 0.80 = 60% of originalYou end up paying 60% of the original, which means the true discount is 40%, not 45%. The second discount applies to the already-reduced price, so it’s worth less in dollars.
On a $100 item: 25% off brings it to $75; another 20% off brings it to $60. You saved $40 total — an effective 40% discount.
To get the real combined rate, multiply the “remaining” fractions: 0.75 × 0.80 = 0.60, so you pay 60% and save 40%. The percentage calculator is handy for checking effective rates on stacked deals.
How to Find the Original Price From the Sale Price
Sometimes you know the discounted price and the percent off, and want the original. Rearrange the formula:
Original = Sale price ÷ (1 − discount ÷ 100)
Example: An item is on sale for $60 after 25% off. What was the original price?
Original = $60 ÷ (1 − 0.25) = $60 ÷ 0.75 = $80So the pre-discount price was $80. This is useful for spotting fake “sales” — if the math doesn’t produce a clean original price, the markdown might not be what it claims.
Reference Table: Percent Off a $100 Item
Here’s what common discounts look like on a $100 purchase:
| Discount | You Save | You Pay |
|---|---|---|
| 5% | $5.00 | $95.00 |
| 10% | $10.00 | $90.00 |
| 15% | $15.00 | $85.00 |
| 20% | $20.00 | $80.00 |
| 25% | $25.00 | $75.00 |
| 30% | $30.00 | $70.00 |
| 40% | $40.00 | $60.00 |
| 50% | $50.00 | $50.00 |
| 60% | $60.00 | $40.00 |
| 70% | $70.00 | $30.00 |
| 75% | $75.00 | $25.00 |
To scale these to any price, just multiply by the price in hundreds — a 30% discount on a $250 item is 2.5 × $30 = $75 off.
Frequently Asked Questions
How do I calculate 20% off a price? Multiply the price by 0.20 to get the savings, then subtract. For $45: $45 × 0.20 = $9, so the sale price is $36. Or just multiply by 0.80 in one step.
Do two discounts add together? No — stacked discounts multiply. “30% off plus 20% off” gives an effective 44% off (0.70 × 0.80 = 0.56, so you pay 56%), not 50% off.
How do I find the original price after a discount? Divide the sale price by (1 − discount as a decimal). A $75 item that was 25% off had an original price of $75 ÷ 0.75 = $100.
Is sales tax added before or after the discount? After. Stores apply the discount first, then charge sales tax on the reduced price. Use the sales tax calculator on the post-discount total.
The Bottom Line
A discount is one multiplication: Sale price = Original × (1 − discount ÷ 100). Anchor your mental math on 10%, remember that stacked discounts multiply rather than add, and divide by the remaining fraction when you need to work backward to the original price. For exact numbers on any markdown — including the savings and final price — run it through the discount calculator, and reach for the percentage calculator when you need to check an effective rate.