Discount Calculator

What a Discount Really Does

A discount is a percentage taken off a price - “25% off” means you keep 75% and pay that. The bar under the calculator splits the original price into what you pay (blue) and what you save (red), with tax added in green if you include it.

Two things trip people up, and the tool handles both: sales tax is added after the discount, and two stacked discounts (say 20% off, then an extra 10% off) do not add up to 30% off. Each discount comes off a smaller amount, so the real total is a little less off than it sounds.

Discount Formula

To take a percentage off a price:

$$\text{discount} = \text{price} \times \frac{\text{percent}}{100} \qquad \text{sale price} = \text{price} - \text{discount}$$

To add sales tax to the discounted price:

$$\text{final price} = (\text{price} - \text{discount}) \times \left(1 + \frac{\text{tax}}{100}\right)$$

For two discounts applied one after the other:

$$\text{final price} = \text{price} \times \left(1 - \frac{\text{first}}{100}\right) \times \left(1 - \frac{\text{second}}{100}\right)$$

How to Calculate a Discount

1. Multiply the price by the percent, divided by 100, to get the amount off.
2. Subtract that amount from the price to get the sale price.
3. To include tax, multiply the sale price by $1 + \text{tax} / 100$.

Worked Examples

Problem	Steps	Answer
25% off a price of 80	80 x (25 / 100) = 20 off	60
30% off a price of 50	50 x (30 / 100) = 15 off	35
40% off 120, then 8% tax	120 - 48 = 72, then 72 x 1.08	77.76
20% then 10% off 200	200 x 0.8 x 0.9	144 (28% off)

Common Uses

• Working out a sale price before you buy.
• Checking a store’s “extra percent off” stacked deal.
• Adding sales tax to a discounted price.
• Comparing two offers quickly.

FAQ

How do you calculate a discount?

Multiply the price by the percent, divided by 100. For example, 25% off 80 is $80 \times (25 / 100) = 20$, so the sale price is $80 - 20 = 60$.

How do you add sales tax to a discounted price?

Take the price after the discount and multiply by $1 + \text{tax} / 100$. For 72 after a discount with 8% tax: $72 \times 1.08 = 77.76$.

Do two stacked discounts add together?

No. 20% off and then 10% off is not 30% off. Each percent applies to a smaller amount, so $200 \times 0.8 \times 0.9 = 144$, which is 28% off overall.