Discount Calculator

sale price = original x (1 - discount), then x (1 - second discount), then less any dollars off. The part worth knowing: percentages stack multiplicatively, not additively. 20 percent off followed by 10 percent off leaves you paying 0.8 x 0.9, which is 0.72 of the original - a 28 percent discount, not 30. The bigger the two numbers, the bigger the gap: 50 and 50 is 75 percent off, not free. Order matters for dollars-off coupons but not for percentages. Two percentages give the same answer either way; a dollars-off coupon is worth more applied before a percentage than after it, which is why stores apply it after.

How do I calculate a percent off in my head?

Ten percent is the decimal point moved one place. Build the rest from that: 20 percent is double it, 30 percent is triple, 15 percent is ten plus half of ten. For 25 percent, quarter it instead. On $89.99, ten percent is $9, so 30 percent is about $27 off, leaving about $63.

Why is 20% off then 10% off not 30% off?

Because the second discount is taken from the price after the first one. On $100, 20 percent off leaves $80, and 10 percent of $80 is $8, not $10. You pay $72, so the real discount is 28 percent. Stacked coupons are always worth slightly less than they sound.

Is "buy one get one 50% off" the same as 25% off?

Yes, if you buy two. Two items at full price is 2.0, one full and one half is 1.5, and 1.5 divided by 2 is 0.75 - a 25 percent discount across the pair. If you only want one item, it is no discount at all.

Is the discount applied before or after sales tax?

Before, in every US state. Tax is charged on what you actually pay, so a discount saves you the tax on the discounted amount as well. That makes a discount slightly more valuable than it first appears, by exactly your tax rate.

How do I work out the original price from a sale price?

Divide, do not multiply back. If $60 is 25 percent off, the original is 60 / 0.75, which is $80. Adding 25 percent to $60 gives $75 and is wrong, because the percentage was of the larger number.