Percentage calculator

To find a percent of a number, divide the percent by 100 and multiply: 15% of 200 = 0.15 × 200 = 30. To find what percent X is of Y, divide X by Y and multiply by 100. Percent change is (new − old) ÷ old × 100. Pick the question below and the calculator shows the working.

By Sunil Arora · Updated · How we calculate

  • 4 percentage questions
  • Working shown
  • Negative percents
  • Shareable link

Your numbers

%

15% of 200

30

Working
1Formula15 ÷ 100 × 200
2Answer30
Assumptions behind this estimate (1)
  • Quick check: 10% of a number moves the decimal one place left; 5% is half of that.

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How do I calculate percent change?

Subtract the starting value from the new value, divide by the starting value, and multiply by 100. A price that rises from $50 to $65 has gone up (65 − 50) ÷ 50 × 100 = 30%. A fall from $80 to $60 is (60 − 80) ÷ 80 × 100 = −25%.

Always divide by the starting value. That is why a 50% fall followed by a 50% rise leaves you 25% below where you started.

Percent vs percentage points

When a rate moves from 3% to 5%, it rose by 2 percentage points — but by 66.7% in relative terms. Interest rates, tax rates and poll numbers are usually compared in percentage points.

How do I reverse a percentage?

If you know the result and the percent, divide. If 15% of a number is 45, the number is 45 ÷ 0.15 = 300. If a price after 20% off is $80, the original price was $80 ÷ 0.80 = $100. For sale prices with several discounts, use the discount calculator.

How to calculate a percentage

  1. 1Write the percent as a decimal: divide by 100 (15% → 0.15).
  2. 2Percent of a number: multiply the decimal by the number (0.15 × 200 = 30).
  3. 3What percent X is of Y: divide X by Y, then multiply by 100 (30 ÷ 120 × 100 = 25%).
  4. 4Percent change: subtract the old value from the new one, divide by the old value, multiply by 100.

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Frequently asked questions

What is the fastest way to work out a percentage in my head?

10% moves the decimal one place to the left, 5% is half of that and 1% moves it two places. Combine them: 15% of 240 is 24 + 12 = 36.

How do I add a percentage to a number?

Multiply by 1 plus the percent as a decimal. A 20% increase on 500 is 500 × 1.20 = 600. To take a percentage off, multiply by 1 minus the decimal: 30% off 1,000 is 1,000 × 0.70 = 700.

Can a percent change be more than 100%?

Yes. Going from 20 to 50 is a 150% increase. A decrease can’t go below −100%, because that would mean falling below zero.

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