Guide
Percentage Change vs Percentage Difference
The formulas look similar, but the denominator answers a different question. Use percentage change when one value is the baseline. Use percentage difference when neither value is the baseline.
Percentage change is directional
Use (New − Original) ÷ Original × 100. The Original value is the baseline. From 80 to 100: (100 − 80) ÷ 80 × 100 = 25%, so the result is a 25% increase.
Percentage difference is symmetric
Mycelgrid uses the average-denominator convention: |A − B| ÷ ((A + B) ÷ 2) × 100. For 50 and 75, the absolute difference is 25 and the average is 62.5, so the result is 40%. Swapping A and B does not change the answer.
Why the denominator matters
In percentage change, dividing by Original preserves direction relative to the starting point. In percentage difference, dividing by the average treats the two values as peers. Percentage difference is not uniquely defined in every field, so this calculator states its convention explicitly.
Percentage points are a third idea
If a rate moves from 40% to 50%, the difference is 10 percentage points. Relative percentage change is (50 − 40) ÷ 40 × 100 = 25%.
Zero edge cases
Percentage change is undefined when Original is zero. Under the average-denominator percentage-difference convention, 0 and 0 are undefined because their average is zero; 0 and 10 produce 200%.
When another tool is better
Sale discounts, percent error, margin/markup, taxes, finance rates, body measurements, and grade conversions have domain-specific jobs beyond this general calculator.