Percentage Calculator
Percent of, percent-of-total, and percent change.
- Answer
- 10
- Formula
- (20 ÷ 100) × 50
- Summary
- 20% of 50 is 10.
Percentage Calculator handles the three percentage questions people search for most: what a percent of a number is, what percent one number is of another, and how much a value has changed in percentage terms. Everything runs locally in your browser for instant, private results.
How it works
Pick a calculation mode, enter the two numbers it needs, and the result updates instantly. Each mode shows the formula used and a plain-language summary alongside the numeric answer.
Benefits
- Covers three percentage modes in one tool
- Shows the exact formula behind every answer
- Updates instantly as you type, no submit button
- Handles negative numbers and decimals correctly
Use cases
- Work out a tip, discount, or markup amount
- Check what fraction of a budget a cost represents
- Measure percent change in sales, weight, or metrics
- Verify homework or spreadsheet percentage formulas
Best practices
- Use percent change (not isWhatPercent) when comparing before/after values
- Double-check which number is the base in isWhatPercent mode
- Remember percent change can exceed 100% for large increases
- Round display values only after copying the precise formula result
Common mistakes
- Swapping X and Y in the isWhatPercent mode
- Assuming percent change is symmetric between increase and decrease
- Using percent change with a zero starting value
- Forgetting the answer sign indicates increase or decrease
Privacy
All arithmetic runs locally in your browser. Percentage Calculator does not transmit your numbers to any server, and nothing is stored unless you opt into on-device history.
Frequently asked questions
- What calculations does this percentage calculator support?
- Three common modes: finding X% of a value, working out what percent one number is of another, and calculating the percent change between a starting and ending value.
- How is "X% of Y" calculated?
- The tool divides the percent by 100 and multiplies by the base value, so 20% of 50 is (20 ÷ 100) × 50 = 10.
- How is "X is what % of Y" calculated?
- It divides X by the total Y and multiplies by 100. For example, 45 is (45 ÷ 180) × 100 = 25% of 180.
- Why does percent change use the absolute value of the starting number?
- Taking the absolute value of the starting number keeps the sign of the result meaningful (increase vs decrease) even when the starting value is negative.
- Can I use negative numbers or decimals?
- Yes. All three modes accept negative numbers and decimals; only the total or starting value in the isWhatPercent and change modes cannot be zero.
- Does this tool upload or store my numbers?
- No. All calculations happen locally in your browser using plain JavaScript arithmetic. Nothing is sent to a server.
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