I disagree with your formule. Formule should be as follows:

iif(SumX = 0, 0.00%, round(((SumX-SumY)/SumY)*100,2)) gives you the correct percentage increase or decrease.

What is the percentage increase in amount from 90,000 to 100,000 - it is not 10% which is the result from your formule, it is 11.1%.