Retail math has two steps that people often blur together: the discount reduces the price, and sales tax is charged on the reduced price — not the original one.
Enter the original price, the discount percentage and your sales tax rate. You get the amount saved, the tax due on the lower price, and the final amount you pay.
For informational purposes only — not financial advice.
How to use
- Enter the original price before any discount.
- Enter the discount percentage from the tag or promotion.
- Add your sales tax rate if you want the real checkout total, or leave it at zero to ignore tax.
- Press Compute to see the savings, the tax and the final price.
- Compare the final price against a competitor's price, not the headline discount.
Frequently asked questions
How do I calculate a discount?
Multiply the original price by the discount percentage and divide by 100 to get the savings, then subtract that from the original price. At 25% off, an $80 item saves $20 and costs $60.
Is sales tax charged before or after the discount?
After. Tax applies to the reduced price the customer actually pays, which is why a discount saves a small amount of tax as well as the discount itself.
What is the difference between 20% off and then a further 10% off?
They stack multiplicatively, not by addition. A $100 item at 20% off is $80, and a further 10% off that is $72 — not $70. Successive discounts always come off the already-reduced price.
How do I find the original price when I only know the sale price?
Divide the sale price by 1 minus the discount as a decimal. A $60 sale price at 25% off means 60 ÷ 0.75 = $80 as the original price.
Do buy-one-get-one offers work with a discount calculator?
Yes, if you convert them to a percentage first. Two-for-one is effectively 50% off when you buy two items; three-for-two is about 33% off. Enter the equivalent percentage here.
Should I use the discount percentage or the final price to compare deals?
Compare final prices, including tax and any shipping. A larger percentage off an inflated original price can still cost more than a smaller discount elsewhere, which is why the final figure is the honest comparison.