Percentage Calculator

What This Calculator Does

Percentages are everywhere: discounts, taxes, tips, test scores, financial reports. This tool converts any value into the common denominator of 100, letting you compare outcomes across different categories without second-guessing the math.

The calculator supports four modes that cover the most common percentage questions people face daily.

X% of Y: Finding a portion

This mode answers "What is 15% of 200?" It multiplies the number by the percentage divided by 100. For example, 15% of 200 equals 30. Use this for calculating tips at restaurants, figuring out sale discounts, or determining how much of your budget goes to a specific category.

A is what percent of B: Finding a share

This mode answers "What percentage is 45 of 180?" It divides A by B and multiplies by 100. The answer: 25%. Use this when you need to know what portion one number represents of another, like calculating your test score percentage or determining what share of total sales came from one product.

Percent Change: Measuring growth or decline

This mode tracks progression between an old value and a new value. The formula is ((new - old) / old) x 100. A positive result means growth; negative means decline. Use this for salary increases, price changes over time, or tracking performance metrics month over month.

Percent Difference: Symmetric comparison

Unlike percent change, this mode treats both values equally. It divides the absolute difference by the average of both numbers. Use this when comparing two values without declaring either as the baseline, like comparing proposals from two vendors or two competing data points.

Common Mistakes to Avoid

• Forgetting the decimal: Entering "25" as a decimal instead of a percentage gives results 100 times too large. This calculator handles the conversion automatically.
• Swapping numerator and denominator: In "A is what % of B" mode, putting numbers in the wrong order gives misleading results. Double-check which value is the reference.
• Using percent change when symmetric comparison is needed: Percent change depends on which number is "old." If neither number is a baseline, use percent difference instead.
• Division by zero: If your old value or reference is zero, the calculation fails. Ensure inputs represent measurable quantities.

Real-World Applications

• Shopping: A 25% discount on a $180 jacket saves $45. The calculator shows both the savings and the final price.
• Taxes: A 7% sales tax on $320 adds $22.40. Knowing this helps you budget accurately.
• Finance: A 6% annual return on $10,000 yields $600. Compare this across investment options easily.
• Salary: A 3% raise on $55,000 means $1,650 more per year. HR teams use this to benchmark against market rates.
• Reports: Showing that conversion rate improved from 2.8% to 4.0% tells a clear growth story to stakeholders.

Privacy and Accuracy

All calculations happen in your browser. Your numbers are never sent to a server or stored anywhere. The tool rounds results for display, but retains precision during intermediate calculations. For scientific work requiring more decimal places, consider specialized software.