Online Percentage & Ratio Calculator
Calculate percentage of numbers, price discounts, percentage difference, and solve proportion equations a/b = c/x with mathematical precision.
15% × 200 = (15 / 100) × 200 = 30How to use
- Select calculation mode (percent of value, percentage ratio, discount/tax markup, or proportion solver).
- Enter input numbers.
- Get clear calculated answer with formula steps.
Calculation Examples
Find 20% of 500 → 100.
Determine percentage ratio: 50 out of 200 → 25%.
Increase 200 by 10% → 220.
Solve proportion 2/4 = x/10 → x = 5.
Calculation Methodology
A percentage represents one hundredth (1% = 0.01). Cross-multiplication applies for proportions a/b = c/d such that a * d = b * c.
Frequently Asked Questions
How do you calculate a percentage of a number?
Multiply the number by the percentage rate and divide by 100 (e.g., 20% of 500 = 500 * 20 / 100 = 100).
How do you calculate a retail discount?
Multiply original price by discount percentage, divide by 100, and subtract that amount from original price.
What is a mathematical proportion?
An equation stating that two ratios are equal: a/b = c/d, where cross products a*d and b*c are identical.
How to calculate percentage change?
Subtract the old value from the new value, divide by the old value, and multiply by 100%.
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