Percentage Calculator

"Percent" means "per hundred" - a language invented for exactly the questions of daily life: what share, what score, what change. Discounts say "20% off", tips say "15%", taxes say "7.5%", exams say "84% correct". Yet the arithmetic hides a dozen failure modes: moving the decimal, dividing the wrong way, multiplying the wrong numbers, forgetting the sign.

Percentage Calculator covers the three questions that matter - X% of Y, X as a percent of Y, and the change from X to Y - each with the formula stated and the working shown line by line. Decimals, negatives and adjustable precision included. The answer is never just a number: it is a number you can see being built.

• Three modes: Percent of a number, what-percent-is-it, and percent change.
• Formula always shown: The working is visible, never hidden.
• Decimals and negatives: Fully supported, with sign conventions explained.
• Adjustable precision: Up to 10 decimal places.
• Instant results: Updates as you type or switch modes.
• Copy or download: Results ready for documents.
• Free and private: Everything runs in your browser; nothing is uploaded.

1. Pick the mode - what you want to find out determines the formula.
2. Enter the two values the mode needs.
3. Read the result as it appears instantly.
4. Follow the working - the formula and each step are shown.
5. Adjust precision if the answer needs fewer or more digits.
6. Copy or download the result.

Example 1 - A discount. Mode "X% of Y": 20% of 85. The answer is 17 - the exact amount off, with (20/100) x 85 shown.

Example 2 - A tip. Mode "X% of Y": 15% of 80 = 12, the tip on the bill.

Example 3 - A test score. Mode "X is what % of Y": 42 of 50 is 84%, with (42/50) x 100 shown.

Example 4 - A price move. Mode "change from X to Y": 80 to 100 is a 25% increase; reverse it to 100 to 80 and get a 20% decrease - the base matters, and the tool shows both honestly.

Example 5 - A tiny share. Mode "X is what % of Y": 3 of 4000 is 0.075% - a percentage small enough that most mental math would simply round it away.

• Everyday coverage: The three questions that real life asks.
• Transparent working: Formulas shown, not hidden.
• Handles the tricky cases: Decimals, negatives, tiny percentages.
• Two change directions: Increase and decrease both explained.
• Instant and live: No button presses, no waiting.
• Free and private: Runs entirely in the browser with nothing uploaded.