Percentage Calculator

Five common percentage calculations on one page. Results update as you type, and nothing you enter leaves your browser.

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Percentage of a number

What is% of30

What percent is X of Y

is what % of20%

Percentage change

Fromto+25%

Increase by a percentage

increased by%230

Decrease by a percentage

decreased by%170

How to use this percentage calculator

  1. Pick the row that matches your question, such as “What is 20% of 150?” or “From 80 to 100”.
  2. Type your numbers into the two boxes. You can paste values with thousands separators like 1,250.
  3. The result appears right away on the same line. Use Copy to paste it somewhere else.

Each row works on its own, so you can keep several calculations on the screen and compare them.

The formulas behind each calculation

Question Formula Example
What is X% of Y? Y × X ÷ 100 20% of 150 = 30
X is what % of Y? X ÷ Y × 100 30 is 20% of 150
Percentage change from A to B (B − A) ÷ |A| × 100 80 → 100 = +25%
Increase Y by X% Y × (1 + X ÷ 100) 200 + 15% = 230
Decrease Y by X% Y × (1 − X ÷ 100) 200 − 15% = 170

A percentage is a ratio expressed as a fraction of 100. The word comes from the Latin per centum, meaning “by the hundred”. Converting between a percentage and a decimal is always a matter of dividing or multiplying by 100: 15% = 0.15 and 0.15 = 15%.

Worked examples

Shopping discount. A jacket costs $180 and is 35% off. The discount is 35% of 180 = $63, so you pay 180 × (1 − 0.35) = $117.

Test score. You answered 42 of 48 questions correctly. 42 ÷ 48 × 100 = 87.5%.

Price change. A monthly subscription goes from $12.99 to $15.99. The change is (15.99 − 12.99) ÷ 12.99 × 100 ≈ +23.1%.

Salary raise. A salary of $64,000 gets a 4.5% raise. 64,000 × 1.045 = $66,880.

Common mistakes to avoid

  • Using the wrong base for percentage change. Always divide by the starting value. Going from 50 to 75 is +50%, but going from 75 back to 50 is about −33.3%.
  • Adding percentages that apply to different bases. Two successive 10% increases are a 21% total increase (1.1 × 1.1 = 1.21), not 20%.
  • Confusing percent with percentage points. When an interest rate moves from 3% to 4%, it rose by 1 percentage point, but by 33.3% in relative terms.
  • Reversing a discount. To find an original price after a 20% discount, divide by 0.8 instead of adding 20% back. A $80 sale price came from $100, not $96.

Glossary

  • Base (whole) – the reference value a percentage is taken from.
  • Part – the portion of the base you are comparing.
  • Percentage point – the arithmetic difference between two percentages.
  • Relative change – a change expressed as a percentage of the starting value.

Privacy

All calculations run in JavaScript on your device. The numbers you type are not sent to a server or stored.

Frequently asked questions

How do I calculate a percentage of a number?

Divide the percentage by 100 and multiply by the number. For example, 20% of 150 is 0.20 × 150 = 30.

How do I find what percent 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%.

What is the formula for percentage change?

Percentage change = (new value − old value) ÷ |old value| × 100. Going from 80 to 100 is a change of (100 − 80) ÷ 80 × 100 = +25%.

Why doesn't a 20% increase followed by a 20% decrease bring me back to the start?

Because the second percentage is applied to a different base. 100 increased by 20% is 120, but 20% of 120 is 24, so decreasing it gives 96, not 100.

What is the difference between percent and percentage points?

Percentage points measure the plain difference between two percentages. A rate that moves from 4% to 5% rose by 1 percentage point, which is a 25% relative increase.

Can I calculate a percentage change from zero?

No. Percentage change divides by the starting value, so a change from 0 is undefined. The calculator shows a dash in that case.

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