Discount calculator
Percent off, the price before the discount, and stacked discounts, with the arithmetic shown so you can check every number. Free, nothing stored.
The price before anything comes off.
The percentage on the label, between 0 and 100.
Changes the symbol on screen. No conversion happens.
Enter a price and a discount. The final price appears as you type, with the arithmetic underneath. A discount of 20% means you pay 80% of the price, so one multiplication does the whole job. Or .
What it used to cost.
What it costs now.
Changes the symbol on screen. No conversion happens.
Enter the old price and the new one, and you get the percentage off plus the amount saved. If the new price is the higher one, you get the increase instead, clearly labelled. Or .
What you are being asked to pay now.
The percentage that was taken off. Below 100, because 100% off cannot be reversed.
Changes the symbol on screen. No conversion happens.
Enter the sale price and the discount that was applied, and you get the price before the discount. The sum divides rather than adds, which is why putting the percentage back on by hand never returns you to the same number. Or .
Leave it blank to see the effective discount on its own.
Changes the symbol on screen. No conversion happens.
Enter two or more discounts to see what they really come to. Successive discounts multiply rather than add, so 20% off followed by an extra 10% off is not 30% off. A price is optional here. Or .
How to work out a discount
- Turn the percentage into a decimal by dividing it by 100. A 20% discount becomes 0.20. That decimal is the share of the price the discount takes off, and every sum below is built from it.
- Multiply the original price by that decimal to get the saving. On a price of 279, that is 279 × 0.20 = 55.80. This is the money that comes off, not the money you pay.
- Subtract the saving from the original price to get what you pay: 279 - 55.80 = 223.20. The one-step version is to multiply by what is left instead of what comes off, because a 20% discount leaves 80% behind: 279 × 0.80 = 223.20, the same answer with one step fewer. Multiplying by what is left is also the only version that survives a second discount, which is the next section.
Why 20% off then 10% off is not 30% off
An extra discount is taken off the price that is already reduced, never off the price on the ticket. That single fact is why the two percentages cannot be added together, and it is worth more than any calculator, because it is the mistake that makes a sale look better than it is. Here it is on a price of 279.
- 20% off 279
- 279.00 × 0.80 = 223.20
- Then 10% off that
- 223.20 × 0.90 = 200.88
- Both multipliers
- 0.80 × 0.90 = 0.72
- Effective discount
- (1 - 0.72) × 100 = 28%
- A real 30% off
- 279.00 × 0.70 = 195.30
You pay 200.88. A genuine 30% off would have been 195.30, so the stacked offer is 5.58 worse than the number in your head, on one item. The reason is in the third line: what survives a discount is a multiplier, and multipliers combine by multiplying. Twenty percent off leaves 0.80 of the price, another ten percent off leaves 0.90 of what was left, and 0.80 × 0.90 = 0.72. You pay 72% of the original, which is 28% off.
The general rule is one line: multiply what is left after each discount, then subtract that product from 1. Effective discount = 1 - (1 - d1) × (1 - d2) × ... and so on for as many as you are offered. It works for three or four stacked offers exactly as it works for two, which is what the stacked tab in the calculator above does with your own numbers.
The gap grows as the discounts get bigger. Take 20% off followed by 15% off: 0.80 × 0.85 = 0.68, so you pay 68% of the price and the real discount is 32%, not the 35% that adding them up suggests. On 279 that is 189.72 rather than 181.35, a difference of 8.37. Push it to the extreme and the point becomes obvious: 50% off twice is not 100% off, it is 0.50 × 0.50 = 0.25, so you still pay a quarter of the price. Nothing is ever free from two half price offers.
One thing that does not matter is the sequence. Taking the 10% first gives 279 × 0.90 = 251.10, and 20% off that is 200.88, the same price as before. Multiplication gives the same product whichever way round you do it, so a shop cannot make a stacked offer worth more or less by reordering it.
Does the order of discount and tax matter?
No. This is the question people worry about most at the till, and the answer is settled by the arithmetic rather than by opinion. Here is 279 with a 20% discount and 8% sales tax, worked both ways with the same numbers.
Discount first, then tax
- 279.00 × 0.80 = 223.20
- 223.20 × 1.08 = 241.06
Tax first, then discount
- 279.00 × 1.08 = 301.32
- 301.32 × 0.80 = 241.06
Both land on 241.06. They have to, because both are the same product written in a different sequence: 279 × 0.80 × 1.08 and 279 × 1.08 × 0.80. Multiplication is commutative, so the order the two rates are applied in cannot change what you pay. The only thing that can ever separate the two answers is rounding, since each rounding step can move a figure by up to a cent, which is why the calculator above carries full precision through the chain and rounds once at the end.
What genuinely changes the total is the base the tax is charged on, not the order. If tax is charged on the discounted price, then a bigger discount also means less tax, and both savings land in the same direction. If it is charged on the full price, the tax stays where it was no matter how large the discount is. That is a rule about what is being taxed, and it is worth checking on the receipt rather than assuming.
Frequently asked questions
How do I calculate a 20% discount?
Multiply the price by 0.80. That is 100% minus 20% written as a decimal, and it gives you what you pay in one step: 279 × 0.80 = 223.20. If you want the saving rather than the price, multiply by 0.20 instead: 279 × 0.20 = 55.80. The two answers add back to the price you started with, 223.20 + 55.80 = 279, which is the quickest way to check yourself.
How do I find the original price from a sale price?
Divide the sale price by 1 minus the discount as a decimal. A price of 189.72 after 32% off is 189.72 / 0.68 = 279. The tempting shortcut is to add the percentage back onto the sale price, and it does not work: 189.72 plus 32% is 250.43, which is nowhere near where you started. A percentage is always a share of the number it was taken from, and this discount was taken from the original price, not from the sale price.
Do two discounts add together?
No, they multiply. A 20% discount followed by an extra 10% off the reduced price leaves you paying 0.80 × 0.90 = 0.72 of the original, which is 28% off rather than 30%. On a 279 price that is 200.88 instead of the 195.30 a true 30% would give you, a gap of 5.58. The rule holds for any number of discounts: multiply what is left after each one, then take that product away from 1 to get the discount you actually received.
Should tax be applied before or after the discount?
For the final price it makes no difference. Taking 20% off and then adding 8% tax gives 279 × 0.80 × 1.08 = 241.06, and adding the tax first gives 279 × 1.08 × 0.80 = 241.06. Multiplication gives the same product whichever way round you do it, so the order cannot change what you pay. What does change the answer is the base the tax is charged on: if tax is charged on the discounted price, a bigger discount lowers the tax as well.
Do you store what I type?
No. Every sum on this page runs in your browser, there is no server route behind the calculator, and nothing you type is sent anywhere or saved. Reload the page and it is gone. If you want to keep a result, use the copy button and paste it somewhere of your own.