字幕表 動画を再生する 英語字幕をプリント How to Calculate Sales Tax. The price on the tag is probably not the price you will end up paying. Follow these steps to determine how much your new purchase will really cost. You will need Purchase price Sales tax percentage Basic math skills and calculator (optional). Step 1. Determine the purchase amount of the taxable items you will buy. Subtract all coupons and discounts. Step 2. Determine the sales tax rate percentage, which will vary state-to-state. Step 3. Turn the percentage into a decimal. Move the decimal place two spaces to the left of the number. For example 12.5 percent would equal .125 and 6 percent would equal .06. Step 4. Multiply the purchase price and the sales tax decimal to calculate the sales tax amount. Use a calculator if needed. Step 5. Add the sales tax amount to the purchase price for the total amount due, and enjoy knowing what you paid before the cashier does. Did you know As of 2010, the state of California had the United States' highest sales tax rate at 8.25 percent.