Percentage Calculator

Each mode covers a different everyday percentage question. 'X% of Y' multiplies Y by X/100 to find a portion of a value — useful for tips, discounts or commission. 'X as a percentage of Y' divides X by Y and multiplies by 100 to express one number as a share of another — useful for grades, quotas or budgets. 'Percentage change' takes ((new − old) / old) × 100 to measure growth or decline between two values.

These three calculations come up constantly outside finance too: working out a test score, tracking a weight change over time, comparing a growth rate between two periods, or checking how much a bill increased year over year.

Percentage change gets confusing with negative numbers or when the starting value is zero, since dividing by zero is undefined. It's also worth remembering that percentage increases and decreases aren't symmetric — a 50% increase followed by a 50% decrease doesn't return you to the original number, because the decrease is applied to a larger base.