Understand the base and formula

Percentage guides without hidden assumptions

Three focused guides explain how to choose the base, distinguish common comparison metrics, and reverse a known percentage change.

Percentage foundations6 min read

How to choose the base for a percentage calculation

Learn which number belongs in the denominator for percentage-of, ratio, and percentage-change questions.

Comparing values6 min read

Choose the comparison metric that matches direction, symmetry, or a difference between two rates.

Inverse percentages6 min read

Recover an original value by dividing by the change multiplier instead of applying the opposite percentage.