Four percentage questions — four different formulas
Percentage calculations are often grouped under one name even though they answer different questions. Toolmera separates them into four modes so the inputs and formula match the problem you are actually solving.
Use “X is what % of Y?” for part-of-a-whole questions, “What is X% of Y?” to calculate a percentage of a number, “Increase / decrease” for before-and-after change, and “Percentage difference” when comparing two values without treating either one as the original.
The formulas, with quick examples
Part of a total uses (Value ÷ Total) × 100. For example, 42 out of 60 is 70%. A percentage of a number uses Number × (Percent ÷ 100), so 20% of 80 is 16.
Percentage change uses ((New − Old) ÷ |Old|) × 100. Percentage difference uses the absolute difference divided by the average magnitude of the two values, then × 100. Toolmera shows the active formula beneath the result.
Percentage change vs. percentage difference
Use percentage change when one value is clearly the starting point and the other is the new value. The sign tells you whether the result is an increase or decrease.
Use percentage difference when the two values are peers and neither is the baseline. This is common when comparing two measurements, estimates or experimental results.