How to use it
Type the original price and the percent off, and the sale price appears with the amount you save. Press Add another percent off when a shop takes off a second discount, such as 20% off, then an extra 10% at the till. You can also take an amount off (a coupon, say) and add a sales tax rate to see what you will really pay. Each step is listed, so you can check the receipt. The second tab does the sum backwards: give it the sale price and the percent off, and it finds the price before the discount.
Why 20% and 10% is not 30%
When discounts come one after another, each one applies to the price left by the one before it. 20% off a price of 100 leaves 80, and then 10% off 80 is 8, so you pay 72. That is 28% off in total, not 30%. The tool shows the combined figure whenever you stack discounts. In the same way, 50% off and then another 50% off leaves a quarter of the price: 75% off, not 100%. Amounts off come after the percentages here, and tax is worked out last on the sale price, which is how most shops charge it.
Questions
Is the tax rate included in the sale price? No. It is added on top, only if you type a rate. For prices that already include tax, see the Sales Tax and VAT Calculator. Does it round to cents? Yes, after every step, as shops do. Can I change the currency? Change the symbol; it is remembered on this device. For a plain percentage, use the Percentage Calculator.