Percentage Calculator

What this tool does

The Percentage Calculator answers the six percentage questions people ask most often, from finding 15% of 200 to measuring the change between two prices. Every answer comes with the working, so you can check the arithmetic or copy the method into homework, reports and spreadsheets.

A percentage is simply a fraction with a denominator of 100, yet the same idea appears in very different questions: a 15% tip on a bill, a test score of 42 out of 60, a salary rising from 50,000 to 56,000, or the gap between two lab readings. Each needs a slightly different formula, and mixing them up is the usual reason a percentage answer comes out wrong.

This calculator keeps each question separate. Choose the calculation, enter two numbers and the result updates as you type, together with a line of working such as "30 ÷ 200 × 100 = 15%". Percentage change uses the old value as the reference, while percentage difference uses the average of both values, so it gives the same answer whichever value you list first. All arithmetic happens in your browser.

How to use Percentage Calculator

1. Pick the question you want to answer from the Calculation list, for example "What is X% of Y?".
2. Enter the values in the fields that appear. Decimals and negative numbers are accepted.
3. Read the highlighted result; secondary cards show the remaining share, the decimal form or the multiplier where relevant.
4. Check the working line under the results to see exactly how the answer was produced.
5. Use the copy icon on any result card to paste the number elsewhere, or Reset to restore the example values.

Tips for better results

• To find the original price before a discount, use "X is P% of what?": a sale price of 68 after 15% off is 85% of the original, so enter 68 and 85.
• A 50% rise followed by a 50% fall does not return to the start: 100 becomes 150, then 75. Use the multiplier card to chain changes.
• When neither value is clearly the "before" figure, such as two measurements of the same object, use percentage difference.
• Percentage points and percent are different: an interest rate moving from 4% to 5% is a 1 percentage point rise but a 25% increase.

Common use cases

• Calculating discounts, tips, tax and commission amounts.
• Turning test marks or survey counts into percentages.
• Measuring month-on-month growth in sales, traffic or prices.
• Comparing two experimental readings in a science report.

Common mistakes to avoid

• Dividing by the new value instead of the old value when calculating percentage change.
• Adding percentages from successive changes instead of multiplying the factors (1.10 × 1.10 = 1.21, not 1.20).
• Calculating a percentage change from zero, which is undefined; report the absolute difference instead.