Percentage calculator

The three percentage calculations

Choose the mode and enter the values: the result appears immediately.

Classic pitfalls

A rise and a fall of the same percentage do not cancel out. A price of 100 that rises by 20% goes to 120; if it then falls by 20%, it drops to 96, not 100. The fall applies to a larger base.

Getting back to the start takes a different percentage. After a 20% fall, you need a 25% rise to recover the original value. After a 50% drop, you must double, a +100% rise.

Percentage points versus percent. A rate going from 2% to 3% rises by one point, but by 50% in relative terms. Both statements are correct, but they do not say the same thing.

Discounts and sales

• Price after discount: price × (1 − discount / 100). An item at 80 reduced by 30% costs 80 × 0.70 = 56.
• Stacked discounts: −30% then −20% make −44%, not −50%, because the second discount applies to the already reduced price.
• Finding the original price: sale price ÷ (1 − discount / 100). 56 after −30% corresponds to 56 ÷ 0.70 = 80.

And sales tax or VAT?

Going from a pre-tax price to a price including tax is a rise: 100 before tax with 20% tax gives 120. But to find the pre-tax price from the total, you must divide by 1.2, not subtract 20%: 120 including tax means 100 before tax, whereas 120 − 20% would give 96. Toolo's invoice generator does these calculations automatically.

Frequently asked questions

How do I calculate a discount?

Use "% of a number": the result is the discount amount to subtract from the price. For 25% off 60, the discount is 15, so the final price is 45.

How do I calculate a percentage change?

Use "Change" mode: (final value − initial value) ÷ initial value × 100. A negative result means a decrease.

Why don't −20% then +20% bring me back to the original price?

Because the rise applies to the reduced price, which is smaller than the starting price. You would need +25% to get back to the original value.

Are my calculations sent anywhere?

No, everything is calculated in your browser.