Percentages translate comparisons into a common scale out of one hundred. This calculator is built to answer every routine percentage question without a formula sheet: “what is x% of y,” “x is what percent of y,” “x is y% of what,” “how different are these two numbers,” and “what’s the new value after an increase or decrease.” Every panel updates live as you type and shows both a green final answer and an amber step-by-step explanation so you can verify the math.
How to use it: Start with the panel that matches your phrasing. For discounts or tips, use X% of Y. For grades or conversion rates, try A is what % of B. To back-solve a base price from a percent and final amount, use A is B% of what. For analytics comparisons—two prices, two measurements—use Percent difference. And when a value changes by a rate, use Percentage change to get the new value.
What is a percentage? A percent is a dimensionless ratio per hundred. Writing 37% is shorthand for 37 out of 100, or 0.37 as a decimal. Converting between these forms is the key step in every calculation: divide by 100 to go from percent to decimal; multiply by 100 to go back.
How to find the percentage of a number: Multiply the decimal form of the rate by the base: result = (rate ÷ 100) × base. Example: 17% of 240 is 0.17 × 240 = 40.8.
How to find what percent one number is of another: Divide the part by the whole and multiply by 100: percent = part ÷ whole × 100%. If the whole is zero, the percentage is undefined.
How to find the base from a percent and a part: Rearrange the first formula: base = part ÷ (rate ÷ 100). If 25 is 75% of what number? 25 ÷ 0.75 = 33.333….
Percent difference vs. percent change: Percent difference uses the average of two values as the baseline, making it symmetric and fair when neither number is “the original.” Percent change uses the original value as the denominator, which answers “how much did this thing change from where it started?”
Limits & tips: Round only at the end for accuracy; choose an appropriate number of decimal places for your audience. Watch for division by zero. Consider whether negative signs are meaningful (e.g., losses vs. gains). When compounding multiple changes (e.g., +10% then −10%), remember they do not cancel; apply each multiplicatively.
With the live steps and copy-link feature, you can drop an exact setup into a doc or chat and others will see the same inputs and outputs instantly. For larger analyses (sales tax, compound interest, discounts on top of discounts), check the related tools in the right rail.