Arithmetic, time and navigation
Percentages
Calculate X% of a quantity, what percentage a part represents, or the variation between two values.
Tool
Tools › Arithmetic, time and navigation
How it is calculated
X % of Y = Y × X ÷ 100. Example: 20 % of 50 = 50 × 20 ÷ 100 = 10.
What % is X of Y = 100 × X ÷ Y. Example: 25 out of 200 is 100 × 25 ÷ 200 = 12.5 %.
Variation from one value to another = 100 × (final − initial) ÷ initial. Example: from 80 to 100 is a variation of 100 × (100 − 80) ÷ 80 = +25 %.
Applying an X % = Y × (1 + X ÷ 100), with X negative to reduce. Example: 200 reduced by 15 % = 200 × (1 − 0.15) = 170.
Keep in mind
- Increasing a value by X % and then reducing it by the same X % does not return the original value (unless X = 0): percentage changes do not cancel out symmetrically.
- For large or repeated changes (compound interest, a reserve growing over time), apply the calculation several times instead of adding up the percentages.