Percentage Calculator
Percentages are one of the most common mathematical tools in everyday life, used in everything from sale discounts and tax rates to exam scores and investment returns. A percentage simply expresses a number as a fraction of 100: saying something is 25% means 25 out of every 100, or one quarter. Despite their ubiquity, percentage calculations can trip people up because there are several distinct questions you might want to answer, and each uses a slightly different formula. The first is the most common: what is X% of Y? The answer is Y multiplied by X divided by 100. The second is the reverse: X is what percentage of Y? Divide X by Y and multiply by 100 to express it as a rate. The third involves change over time: what is the percentage change from X to Y? Subtract X from Y, divide by X, and multiply by 100; a positive result is an increase, and a negative result is a decrease. The fourth applies a percentage directly to a base: if X increases or decreases by Y%, the result is X multiplied by (1 plus or minus Y divided by 100). This calculator handles all four modes simultaneously with independent input fields so you can solve any percentage problem without switching between tools or rearranging formulas yourself.
Mode A: What is X% of Y?
Mode B: X is what percent of Y?
Mode C: Percentage change from X to Y
Mode D: X increased/decreased by Y%
How percentage calculations work
All percentage calculations are built from the basic relationship: percentage = (part / whole) * 100. Rearranging this formula gives us the four modes below.
Mode A: result = Y * (X / 100)
Mode B: result = (X / Y) * 100
Mode C: result = ((Y - X) / X) * 100
Mode D: result = X * (1 + Y / 100)
Worked examples
Mode A: What is 20% of 500?
- 500 * (20 / 100) = 500 * 0.2 = 100
Mode B: 30 is what percent of 150?
- (30 / 150) * 100 = 0.2 * 100 = 20%
Mode C: What is the percentage change from 100 to 120?
- ((120 - 100) / 100) * 100 = (20 / 100) * 100 = 20% increase
Mode D: 200 increased by 15%
- 200 * (1 + 15 / 100) = 200 * 1.15 = 230
Percentage calculator: frequently asked questions
What is a percentage?
A percentage is a number expressed as a fraction of 100. The word comes from Latin 'per centum', meaning 'per hundred'. Percentages are used to express how much of a whole something represents, to compare quantities, and to describe changes. For example, 25% means 25 out of 100, or one-quarter.
How do I calculate what percent one number is of another?
Divide the first number by the second, then multiply by 100. For example, 30 out of 50 is (30 / 50) * 100 = 60%. This calculator does this automatically in Mode B.
What is the difference between percentage and percentage point?
A percentage is a proportion (e.g., 50% of a population). A percentage point is a unit of change: if something rises from 40% to 45%, that is a 5 percentage point increase, or a 12.5% relative increase. This calculator shows both in Mode C.
How is percentage change calculated?
Percentage change = ((new value - old value) / old value) * 100. A positive result means an increase; negative means a decrease. For example, if sales rise from 100 to 120, the change is (120 - 100) / 100 * 100 = 20% increase.
When would I use the percentage increase or decrease tool?
Use it to apply a percentage change to a base value. For example, if an item costs 80 dollars and you get a 15% discount, you multiply 80 by (1 - 0.15) = 80 * 0.85 = 68 dollars. The calculator does this instantly.
Can percentages be greater than 100%?
Yes. A percentage greater than 100% means the result is more than the original whole. For example, if you invest 100 dollars and it grows to 250 dollars, the return is 250% of the original investment (or a 150% gain).
Official sources
- NIST Guide to the SI: NIST Special Publication 330.
- Standard arithmetic definition: basic mathematics principles and operations.
Reviewed by the CalculatorHub team, edited by James Graham, 13 June 2026. See our methodology.