Percentage Calculator
Percentages, increases, and differences made easy.
A percentage is simply a way of expressing a number as a part of 100, and our Percentage Calculator handles the three questions people run into most often. Use the dropdown to switch between finding what A% of B is, working out what percent one number is of another, or measuring the percent change between two values. Just type your two numbers into fields A and B, and the answer updates live as you go.
The math behind every mode comes from one simple relationship: the part equals the percent divided by 100, multiplied by the whole. Whether you are figuring a tip, a discount, a test score, or a price change, this tool keeps the arithmetic accurate and instant so you can focus on the decision instead of the calculation.
Result
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Formula
part = (percent / 100) × wholeHow to use the percentage calculator
- Choose a mode from the dropdown: What is A% of B, A is what percent of B, or percent change from A to B.
- Enter your first number in field A. Its meaning depends on the mode you selected.
- Enter your second number in field B to complete the calculation.
- Read the result, which updates live as soon as both fields contain valid numbers.
- Switch modes or edit either value to run another calculation without clearing the page.
Worked example
Suppose a jacket is listed at 80 dollars and the store is offering 25 percent off. Pick the first mode, "What is A% of B," then enter 25 in field A and 80 in field B. The calculator multiplies 25 divided by 100 by 80, which equals 20. That 20 dollars is your discount, so you would pay 80 minus 20, or 60 dollars. If you instead wanted to confirm the discount rate, the second mode shows that 20 is 25 percent of 80.
Common mistakes to avoid
- Mixing up which number is A and which is B, especially in the "A is what percent of B" mode where B is the whole.
- Confusing a percentage-point change with a percent change, for example a rate moving from 5 percent to 6 percent is one point but a 20 percent increase.
- Entering a value that already includes the percent sign or a comma, since only plain numbers are needed.
- Assuming a percent increase and the matching percent decrease cancel out, when they usually do not return you to the original value.
Frequently asked questions
How do I calculate a percentage increase?
Subtract the old value from the new, divide by the old value, then multiply by 100.
What is the difference between the three modes?
The first mode finds a portion, such as 15 percent of 60. The second tells you what percent one number is of another, like what percent 9 is of 60. The third measures how much a value grew or shrank between a starting number and an ending number.
Can the percent change result be negative?
Yes. In the percent change mode, if B is smaller than A the result is negative, which signals a decrease. For instance, going from 200 to 150 shows a change of negative 25 percent, meaning the value dropped by a quarter.
How is this different from a compound interest calculator?
This tool applies a single percentage in one step. If you need to see a value grow repeatedly over time, such as savings earning interest each year, try our <a href="/tools/compound-interest-calculator/">compound interest calculator</a> instead. You may also find our <a href="/tools/unit-converter/">unit converter</a> handy for related everyday math.