Percentage Calculator
X% of Y, percentage change, percentage difference. All in one.
20% of 150 =
30
A percentage calculator handles the everyday percent questions in one place: what is X percent of Y, what percent is one number of another, and what is the percentage change between two numbers.
Enter your numbers into the mode you need. The tool returns the answer instantly and shows the relationship, so tips, discounts, tax, and changes over time all become quick lookups.
Percentages trip people up mainly because the same word covers several different operations. Separating them, as this tool does, removes the confusion.
How this calculator works
The three core operations use simple formulas. X percent of Y is (X / 100) x Y. To find what percent A is of B, divide A by B and multiply by 100. Percentage change from an old value to a new value is (new - old) / old x 100, which is positive for an increase and negative for a decrease. Percentage difference, used when neither value is a baseline, divides the absolute difference by the average of the two values and multiplies by 100. The calculator applies the right formula for the mode you choose and displays the result.
What affects the number
- Choosing the right operation matters; percent of a number, percent change, and percent difference are not the same.
- For percentage change, which value is the baseline (the old one) determines the result.
- Percentage points and percent are different: going from 10% to 12% is 2 points but a 20% increase.
- Reverse percentage problems (finding the original before a markup or discount) require dividing, not subtracting.
- Rounding at intermediate steps can shift the final answer, so round only at the end.
- Very large percentage changes from a small base can look dramatic while representing a small absolute change.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For 20% of 150, compute 0.20 times 150, which is 30. The calculator does this in the 'percent of' mode without the manual step.
How do I find percentage change?
Subtract the old value from the new value, divide by the old value, and multiply by 100. From 80 to 100 is (100 - 80) / 80 x 100 = 25% increase. A negative result means a decrease.
What is the difference between percent and percentage points?
Percentage points measure the arithmetic gap between two percentages, while percent measures relative change. Moving from 10% to 15% is a rise of 5 percentage points, but a 50% increase in relative terms. Mixing them up is a common source of error.
How do I reverse a percentage?
To find an original price before a discount, divide the final price by (1 minus the discount as a decimal). A price of $80 after 20% off was $80 / 0.80 = $100. For a markup, divide by (1 plus the rate) instead.
This calculator provides general estimates for educational purposes only and is not financial, medical, legal, or tax advice. Your actual results depend on your specific situation and current rates.