I have a list of price data per month and would like to calculate an average of all available data points on a monthly basis upon availablity of a new data point (e.g. in May the average price for Jan - May, in June, average price from Jan - June). Additionally, I need these data to be recalculated by calling off a different month from the drop-down list. For example, if I choose February, it shows average Jan-Feb.

Thanks,
Ksenia