Percentage Increase and Decrease Worksheets | Download Free PDFs - Cuemath In order to calculate p % of q, use the formula: (p/100) x q = (pxq)/100 Work out the difference (increase) between the two numbers you are comparing. Then divide the increase by the original number and multiply the answer by 100. % Increase = Increase ÷ Original Number × 100. If your answer is a negative number, then this is a percentage decrease.