Discount Calculator

Work out a sale price, a saving or the real % off

Discount Calculator answers the four questions that come up when something is on sale: what it costs after a percentage off, what an amount off works out to as a percentage, what the price was before the discount, and what percentage you’re really getting off when you only know the two prices.

Each question has its own tab, and the answer updates as you type, with a one-line explanation of the sum. It uses plain numbers, so it works with any currency, and the calculation happens in your browser.

How to calculate a discount

1. Pick a tab: Percent off, Amount off, Find original price or Find % off.
2. Type the prices and percentages the tab asks for. Decimals are fine, and the boxes don’t need currency symbols.
3. For a “take an extra 10% off” offer, use Percent off and fill in the optional Extra % off box.
4. Read the highlighted answer and the explanation under it. Each tab keeps its own numbers.

What the four results mean

• Sale price: what you pay after the discount.
• You save: the original price minus the sale price.
• Effective % off: the total discount as a share of the original price. With two discounts this is the combined figure, which is lower than adding the two percentages.
• Rounding: prices you type are rounded to the nearest cent, and amounts are shown to 2 decimal places with your device’s thousands separator. The calculator rounds one amount and works out the other as the difference, so the sale price plus the saving always equals the original price exactly.

When a discount calculator helps

• Shopping: check a shelf price after 30% off, or compare “25% off” with “15 off” on the same item.
• Stacked offers: see what a sale price plus an extra member or coupon discount really comes to.
• Checking a claim: enter the was-price and the now-price to see the actual percentage off.
• Adding tax afterwards: take the sale price to the Sales Tax & VAT Calculator if tax is added at the till.

Tips for accurate discount sums

• An empty box counts as “not entered yet”, not as 0, so you see a prompt rather than a misleading result.
• Percentages above 100 and negative numbers are refused with a message. In Amount off the amount can’t be bigger than the price, and working out a % off needs an original price above 0.
• For general percentage questions, such as a percentage increase, use the Percentage Calculator.

Double discounts and working backwards

Why 20% off plus 10% off isn’t 30% off

An extra discount is taken from the price that’s already been reduced, not from the original. On a price of 100, 20% off gives 80. The extra 10% is 10% of 80, which is 8, so you pay 72 — a total of 28% off, not 30%.

The combined percentage is the two discounts added, minus their product divided by 100: 20 + 10 − 2 = 28. The order doesn’t change the combined percentage.

Finding the price before a discount

If something costs 72 after 20% off, you paid 80% of the original price, so the original is 72 ÷ 0.8 = 90. Adding 20% back to 72 gives 86.40, which is wrong, because the 20% was taken from the bigger, original number. The Find original price tab does the division for you; 100% off has no answer, because every price ends up at 0.

Discount Calculator: common questions