Working with Percentages
A percentage expresses a number as a fraction of one hundred, which makes very different quantities easy to compare on a common scale. Percentages appear everywhere — discounts and sales tax, exam scores, interest rates, tips, and statistics. This calculator brings the three most common percentage problems together so you can solve any of them without rearranging formulas by hand.
The Three Calculation Modes
- What is X% of Y: multiply Y by X and divide by 100. For example, 20% of 150 is 30. This is how you find a discount amount or a tip.
- X is what percent of Y: divide X by Y and multiply by 100. For example, 30 is 20% of 150. This is how you turn a score into a percentage.
- Percentage change: subtract the old value from the new value, divide by the old value, and multiply by 100. A positive answer is an increase and a negative answer is a decrease.
Percentages Versus Percentage Points
It helps to keep two ideas separate. If an interest rate rises from 4% to 6%, that is an increase of two percentage points, but it is a 50% increase in relative terms. Confusing the two is a common source of error in headlines and reports, so always be clear about which one a situation calls for.
How to Use This Calculator
- Select the calculation type from the dropdown.
- Enter your two values in the fields, which relabel themselves to match the chosen mode.
- Read the result along with a plain-language sentence explaining what it means.
Everyday Examples
Shoppers use it to check a sale price, students convert marks into grades, and businesses track month-over-month growth or decline. Because the tool shows the reasoning behind each answer, it doubles as a quick way to learn the underlying method rather than just returning a number you cannot check.