Solve everyday percentage problems — find a percent, a share or a change.
Instant local calculation. Nothing is uploaded.
How do you calculate a percentage?
A percentage is a part divided by the whole, multiplied by 100: percentage = (part ÷ whole) × 100. To find X% of a number, multiply the number by X ÷ 100. For example, 20% of 150 is 150 × 0.20 = 30, and 30 out of 150 is (30 ÷ 150) × 100 = 20%.
Understanding your result
A positive percent change means growth, a negative value means a decrease. Percentages are simply fractions out of one hundred, which makes them ideal for comparing different-sized quantities.
Formula and method
X% of Y = (X ÷ 100) × Y. X is what % of Y = (X ÷ Y) × 100. Percent change = ((New − Old) ÷ |Old|) × 100.
Assumptions and limitations
This tool answers the three standard percentage questions from the numbers you type; it does not check whether a percentage is meaningful for your context. Percentage change is undefined when the old value is zero, since dividing by zero has no result. Results are rounded for display, so chained calculations may differ slightly from exact arithmetic.
Worked example
25% of 200 = 50. 25 is 12.5% of 200. The change from 200 to 250 is a 25% increase.
How to use this tool
- Choose the type of percentage problem from the dropdown.
- Enter the two values the question needs.
- Press Calculate to see the answer and the working.
Common mistakes to avoid
- Confusing “percent of” with “percent change”.
- Dividing by the new value instead of the original when finding change.
- Forgetting that a 50% drop then a 50% rise does not return to the start.
About the Percentage Calculator
The Percentage Calculator handles the three percentage questions people ask most: finding a percentage of a number, finding what percentage one number is of another, and measuring the percentage change between two values.
Who should use this tool
Students, shoppers, business owners and anyone who needs a fast, reliable percentage — for discounts, tips, grades, tax, commission or growth rates.
Benefits
- Answers the three most common percentage questions in one place.
- Shows the working, so you learn the method and not just the answer.
- Handles decimals and negative numbers precisely.
- Runs instantly and offline — nothing leaves your browser.
Practical use cases
- Working out a sale price or how much you are saving.
- Calculating a tip, tax or sales commission on an amount.
- Measuring growth between two figures — sales, marks, weight or followers.
Frequently asked questions
How is percentage change calculated?
Subtract the old value from the new value, divide by the old value, then multiply by 100.
Can it handle decimals and negatives?
Yes. The calculator accepts decimal and negative inputs and reports the result precisely.
Why can't I calculate a percentage change from zero?
Percentage change divides the difference by the original value, and division by zero is undefined in mathematics. A change from zero to any positive number is not a meaningful percentage, because there is no baseline to compare against. Start from a non-zero old value to get a valid result.