Percentage Calculator

Percentages appear everywhere — sale discounts, tax rates, exam scores, investment returns, and statistical data. Despite being a simple concept (parts per hundred), percentage calculations are one of the most commonly searched math operations online because the phrasing can be confusing: 'what is 15% of 80?' and '12 is what percent of 150?' require different formulas.

This calculator handles three types: finding a percentage of a number, finding what percentage one number is of another, and calculating percentage change (increase or decrease) between two values. Results update instantly.

Common real-world scenarios this tool solves: a Black Friday price of $129 marked 35% off (sale price $83.85, savings $45.15); a salary raise from $62,000 to $67,580 (+9% change); a test score of 37 out of 50 questions (74% correct). Each of these uses a different formula, which is why the calculator offers three dedicated modes rather than one-size-fits-all input.

Under the hood, every calculation uses IEEE 754 double-precision floating-point arithmetic, accurate to 15–17 significant digits — far more precision than any real-world percentage problem needs. The only cases where a rounding note appears are when the input has more than 12 decimal places, which is well beyond what any bill, tax rate, or exam score would ever require. Known edge case: percentage change is undefined when the base value is zero, because division by zero has no meaningful answer; the calculator surfaces 'Undefined' in that case rather than showing NaN.

Compared to doing the arithmetic in Excel or a handheld calculator, this tool removes the translation step — you don't need to remember whether to write "=A1*0.15" or "=(B1-A1)/A1", just pick the mode and type the numbers. Pair with the Tip Calculator for restaurant math or the Loan Calculator for financial planning.