There are two ways to calculate a conditional average in Excel, both involve some logic and some special functions.

Excel doesn't have a built-in AVERAGEIF() function, but you can still average values, conditionally.

Calculate the weighted average of interest rates in Microsoft Excel to compute the most accurate average interest rate among a group of lenders who received different rates. When you take a ...

With Excel and data from your broker, however, calculating the average return is fairly easy using the XIRR function. How to calculate average stock returns in Excel ...