Y2 - y1 y1100 your percentage change. Divide that change by the old value you will get a decimal number Step 3. Calculate the difference subtract one value form the other ignore any negative sign.
Now you know the percentage difference formula and how to use it.
Percent Difference calculator uses this formula. Divide that change by the old value you will get a decimal number Step 3. Calculate the average add the values then divide by 2 Step 3. 3 Simple Ways to Calculate Percentages Math 1.