Percentage Calculator

Percentages turn up everywhere once you start looking. Applying a 3.5% raise to a salary, tracking a product's market share as it climbs from 15% to 18%, or working out the sales tax on a $500 purchase are all the same kind of problem at heart. Handling them cleanly is what lets you make sound financial calls and read data accurately in a world where percentages sit behind interest rates and growth forecasts alike.

Three core formulas cover most of what you'll need. To answer 'What is X% of Y?', compute (X/100) * Y. For 'X is what % of Y?', the calculation is (X/Y) * 100. And for 'Percentage change from X to Y?', use ((Y - X) / X) * 100; the calculator divides by the absolute value of X, so a move from -50 to -25 shows as a 50% increase. Each one rescales a fraction or ratio onto a hundred-based scale, which is what makes relative values and changes easy to compare at a glance.

The trap people fall into is mixing up 'percentage of' with 'percentage increase or decrease,' since the base value driving the math is different in each case. Check whether your inputs represent the original amount or the changed amount before you trust the answer. A negative percentage change means a decrease and a positive one means an increase, and your inputs need to be numbers, because text or symbols will break the calculation.