Percentage Calculator
Calculate percentages, changes and differences with exact arithmetic and a clear, substituted formula.
Calculations happen locally in your browser. Your values are not uploaded or saved.What is P% of X?
Signed values and negative percentages are supported.
Formula: X × P ÷ 100
Use a dot or comma as the decimal separator: 1,234 means 1.234, not 1,234 grouped as thousands. No grouping, internal spaces, %, currency signs or scientific notation. Maximum 30 numeric digits, with 12 after the separator. Valid values normalize on blur.
Enter both values or use an example to see a result.
Exact rational arithmetic; only the display is rounded, half away from zero. Copy uses the selected decimal places, without thousands separators or an approximation symbol. A % sign is included only for percentage results.
How to calculate a percentage
- Choose the question you want to answer: percent of, what percent, change, adjust or difference.
- Enter two plain decimal values, or select Use example. Valid inputs calculate immediately.
- Review the result and formula. Adjust decimal places for display, then copy the result or full explanation.
Common percentage examples
- 15% of 200: 200 × 15 ÷ 100 = 30.
- 25 as a percentage of 200: 25 ÷ 200 × 100 = 12.5%.
- Change from 80 to 100: (100 − 80) ÷ 80 × 100 = +25%.
- Increase 200 by 15%: 200 × 1.15 = 230. Decrease it by 15%: 200 × 0.85 = 170.
- Difference between 80 and 100: 20 ÷ 90 × 100 ≈ 22.22%.
Percentage points are not percentage change
Moving from 20% to 25% is an increase of 5 percentage points, but a 25% relative increase: (25 − 20) ÷ 20 × 100 = 25%. Percentage points describe the subtraction of two percentage rates, not the relative change.
Input limits and interpretation
Enter at most 30 numeric digits per value, with at most 12 decimal digits. A dot or comma is the decimal separator; 1,234 means 1.234. No thousands separators or scientific notation. Values normalize only on blur. Blank fields and partial values such as a standalone minus sign are not treated as zero.
Exact rational calculations retain full precision. Display rounding uses half away from zero; changing decimal places does not change the calculation. This is a general mathematical utility, not financial or tax advice. Use a modern browser with JavaScript and BigInt support.
Frequently asked questions
What does a comma mean in my input?
Either a dot or a comma is a decimal separator. For example, 1,234 means 1.234, not one thousand two hundred thirty-four. Thousands separators, mixed separators, scientific notation, currency signs and percent signs are not accepted.
How are results rounded?
Inputs and calculations use exact BigInt rational arithmetic, not binary floating-point approximations. Only the displayed result is rounded to 0–8 decimal places, half away from zero. Approximate results carry an approximation symbol; negative zero displays as zero. Copy result follows your selected display precision.
What is the difference between percentage change and percentage difference?
Change uses the old value as the baseline and can be positive or negative. Difference uses the average of two non-negative values and is symmetric: swapping them leaves the result unchanged. Change requires a positive old value; difference is undefined when both values are zero.
Can I use negative numbers?
Percent of and What percent support signed numbers and percentages. Change requires old > 0 and new ≥ 0. Adjust and Difference require non-negative values, and a decrease cannot exceed 100%.
Are my values uploaded or saved?
Calculations happen locally in your browser. Values are held in memory while you use the page, not uploaded, logged, stored or added to URLs. Switching modes keeps each form until reset; reloading clears all values.
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