Percentage Calculator
Work out a percentage of any amount, plus the value increased or decreased by that percentage.
Result
Percentage of amount
20.00
Amount increased by %
120.00
Amount decreased by %
80.00
How it works
A percentage expresses a number as a fraction of 100, which makes very different quantities easy to compare. Whether you are working out a tip, a discount, a tax or an exam score, the logic is always the same: part ÷ whole × 100. This calculator covers the three everyday cases at once: what X% of an amount is, what you get after increasing an amount by X%, and what you get after decreasing it by X%. Change any input and all three answers update instantly. A classic trap is confusing percentages with percentage points, and forgetting that a rise then an equal fall does not bring you back to the start: +20% followed by −20% leaves you at 96% of the original, because the second percentage applies to a bigger base.
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Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage, then divide by 100. For example, 20% of 150 is (150 × 20) ÷ 100 = 30.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. For example, 30 out of 150 is (30 ÷ 150) × 100 = 20%.
How do I calculate a percentage increase or decrease?
Subtract the old value from the new one, divide by the old value, then multiply by 100. A rise from 80 to 100 is a 25% increase.
What is the difference between a percentage and a percentage point?
Going from 10% to 12% is a rise of 2 percentage points, but a 20% relative increase. Mixing the two is one of the most common numeric mistakes in the news.
Why does +20% then −20% not return to the original value?
Because the −20% applies to the new, larger amount. 100 becomes 120, and 20% of 120 is 24, so you end at 96 — not back at 100.
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