Percentage Difference Calculator
The symmetric percent difference between two values, measured against their average.
The formula
difference % = |a - b| / ((a + b) / 2) × 100
Between 45 and 55: the gap is 10, the average is 50, so the percentage difference is 20%. Swap the numbers and the answer stays the same, which is the whole point.
When to use difference, change or error
Use percentage difference to compare two equal-footing values with no natural order. Use percentage change when one value is the starting point (last month's revenue, the old price). Use percent error when one value is the accepted truth and the other is your measurement.