Discount Calculator – Percent Off, Sale Price & Smart Shopping
Enter the original price and the discount percentage to see what you pay and how much you save. You can also stack a second discount (member card, voucher) and add 10% VAT.
🎯 Real Shopping Scenario Quiz
Question 1: A shirt costs $100, discounted 20%, then an additional 10% off the discounted price. What's the final price?
Step 1: 20% off → Price becomes $80 ($100 × 0.8)
Step 2: Additional 10% off $80 → Final: $72 ($80 × 0.9)
Note: Double discount ≠ Simply adding 20% + 10% = 30%! The real discount is only 28%.
Question 2: You only need 1 item. Which promotion saves you more money?
50% Off: You pay 50% of original price for 1 needed item → Save 50% cash.
Buy 1 Get 1: You pay 100% but get 2 items → If you only need 1, the 2nd is "waste" → No cash savings.
Conclusion: If you only need 1, choose 50% off!
The calculator above gives the sale price and how much you save from the original price and the discount percentage. Use the 5%, 10%… 70% buttons to pick a discount quickly. Tick double discount when a member card or stacked voucher takes an extra percentage off, and tick VAT 10% when the listed price excludes tax. Press Example to load the $100 shirt problem from the quiz.
🏷️ Sale price formula
Let P be the original price and d the discount percentage. Convert the percentage to a decimal by dividing by 100, for example 20% = 0.2.
Mental math tip: 20% off means you pay 80%, so multiply the original price by 0.8. For 35% off, multiply by 0.65.
🔁 Double discounts do not add up
When a store takes d₁% off and a member card takes another d₂% off the reduced price, the two factors multiply:
20% off followed by another 10% off is only a 28% discount, not 30%. The order of the two discounts does not change the result.
🧾 Discounts and VAT
If the listed price excludes VAT, the tax is charged on the discounted price:
Because multiplication is commutative, discounting first and then adding tax gives the same total as adding tax first and then discounting.
💡 Worked examples
Example 1. A single discount
A pair of shoes costs $80 with 15% off.
Example 2. Double discount 30% + 20%
A $120 jacket is 30% off, and a member card takes another 20% off.
Real discount: 1 − 0.7 × 0.8 = 0.44, i.e. 44%, not 50%.
Example 3. Find the discount from two prices
An item was $40 and now sells for $30.
Example 4. Find the original price from the sale price
After 20% off, an item costs $72. The original price is:
Note: do not add 20% of $72 back, because the 20% was taken from the original price, not from the sale price.
📊 Quick reference for a $100 item
| Discount | Multiply by | You save | You pay |
|---|---|---|---|
| 10% | 0.9 | $10 | $90 |
| 15% | 0.85 | $15 | $85 |
| 20% | 0.8 | $20 | $80 |
| 25% | 0.75 | $25 | $75 |
| 30% | 0.7 | $30 | $70 |
| 50% | 0.5 | $50 | $50 |
| 70% | 0.3 | $70 | $30 |
🛍️ Smart shopping tips
- “Up to 70% off” usually applies to only a few items. Check the discount on the item you actually need.
- Buy 1 Get 1 Free only pays off if you will use the second item. If you need just one, 50% off saves more cash.
- Fixed-amount vouchers (for example $10 off orders over $60) favour smaller orders. Convert them to a percentage to compare: 10 / 60 ≈ 16.7%.
- Compare with the pre-sale price. Some stores raise the list price before a sale, so a big percentage is not always a good deal.
- Include shipping in the total cost before comparing stores.
⚠️ Common mistakes
- Adding two discounts. 20% off then 10% off is 28% off, not 30%.
- Confusing “20% off” with “20% of”. 20% off means you pay 80% of the price; 20% of means you pay only 20%.
- Finding the original price by adding the percentage back. Divide the sale price by (1 − d/100) instead.
❓ Frequently asked questions (FAQ)
What is the formula for a sale price?
Sale price equals the original price multiplied by (1 minus the discount percentage divided by 100). For example, $100 with 20% off costs 100 × 0.8 = $80.
How do I find the discount percentage from two prices?
Subtract the sale price from the original price, divide by the original price and multiply by 100%. For example, $40 down to $30 is 10 / 40 = 25% off.
Is 20% off plus an extra 10% off the same as 30% off?
No. The second discount applies to the reduced price, so the real discount is 1 − 0.8 × 0.9 = 0.28, i.e. 28%.
How do I find the original price from the sale price?
Divide the sale price by (1 minus the discount percentage divided by 100). For example, $72 after 20% off means the original price was 72 / 0.8 = $90.
What discount is Buy 1 Get 1 Free equal to?
If you use both items, each one is effectively 50% off. If you only need one, you still pay 100% of the price, so 50% off saves more cash.