How this calculator works
A percentage represents a part of a whole expressed as a fraction of 100. The basic percentage formula connects three values: the percentage, the partial value, and the whole value. When you know any two of these values, you can solve for the third using simple division and multiplication.
The most common form asks "What is X% of Y?" The method is to convert the percentage to a decimal by dividing by 100, then multiply by the whole value. For example, to find 20% of 150: 20 / 100 = 0.20, then 0.20 * 150 = 30. So 20% of 150 is 30.
Another common form asks "X is what percent of Y?" Divide the partial value by the whole value and multiply by 100. For example, if you scored 45 out of 60: 45 / 60 * 100 = 75%.
You can also work backward to find the whole value: "30 is 20% of what number?" Divide the partial value by the percentage as a decimal: 30 / 0.20 = 150.
Common use cases include calculating tips on restaurant bills, determining what portion of a budget has been spent, finding percentage scores on tests, calculating discounts during shopping, and analyzing survey results. In finance, percentages are used to express interest rates, returns, and growth. In education, they standardize scores across different total marks. In data analysis, they make comparisons easier across different sample sizes.
Tips: Always convert percentages to decimals before multiplying or dividing. Remember that 50% equals 0.5, 25% equals 0.25, and 100% equals 1.0. To quickly find 10% of any number, move the decimal point one place to the left. To find 1%, move it two places. Use these shortcuts to estimate percentages mentally before checking with a calculator.
Also try: Percentage Increase Calculator to measure growth from an original value to a new value.