Percentage basics
Core formulas, reverse percentages, conversions and the mistakes people make most often.
Percentage basicsHow to calculate a percentage: the three formulas you need
Every basic percentage question is one of three shapes: find the part, find the percentage, or find the whole. Here's how to tell which one you have.
Percentage basicsHow to find a percentage of a number: three methods
Three ways to find a percentage of a number (decimal, fraction and the 1% method) worked on the same examples, with notes on when each is quickest.
Percentage basicsWhat percent is X of Y? Turning a part and a total into a percentage
To find what percent X is of Y, divide X by Y and multiply by 100. The hard part is knowing which number is Y; here are tests for tricky wording.
Percentage basicsReverse percentages: how to find the original number
To undo a percentage change, divide by the multiplier instead of subtracting the percentage. Why the obvious method fails, and how to check your answer.
Percentage basicsHow to find the whole when you know a part and its percentage
If you know a part and what percentage it is, divide the part by the percentage as a decimal. How to tell this apart from undoing a percentage change.
Percentage basicsPercentages, fractions and decimals: how to convert between them
How to convert between percentages, fractions and decimals in every direction, with a table of common equivalents and how to handle repeating decimals.
Percentage basicsPercentage points vs percent: what's the difference?
When a rate moves from 4% to 6%, it rose 2 percentage points and also 50%. What each number means, and how to report changes without misleading anyone.
Percentage basicsPercentages over 100%: what they mean and when they make sense
A percentage above 100% is correct whenever the part can exceed the whole or a value more than doubles. Here's how to tell when it signals a mistake.
Percentage basicsSeven common percentage mistakes and how to avoid them
Seven percentage mistakes that produce confident wrong answers: wrong base, adding percentages, reversing by subtraction, points vs percent and more, each with a quick check.
Percentage basicsBasis points, per mille and parts per million explained
Basis points, per mille and parts per million are smaller cousins of the percent. How they relate, how to convert them, and where each one is used.