The only difference between Mathematical & excel percentage calculation is, In excel *100 is missing, because in Excel when calculating a percent, you don’t have to multiply the resulting value fraction with 100, since, excel will automatically calculate it to or convert it to percentage format, which will be applied to a cell. Average percentage growth tells us how fast something has grown, and eventually forecasts the future through extrapolation. There are different ways of calculating average growth in Excel (e.g. LOGEST, LINEST, lines of best fit, etc.) and some of these will give different results. Let’s Here’s how to calculate both the CAGR and FAGR growth rates in Excel… How to Calculate the Compound Annual Growth Rate in Excel. As shown at the right, to calculate CAGR you divide the ending value by the beginning value to find one plus the total growth percentage during the time of the investment.