Calculate average of the last valid 30 days

I need to calculate a 30 day rolling average.

The difficulty lies in the fact that a day must meet a certain criteria to be considered in the average. If a day does not meet the criteria, the calculation needs to perform as if that day did not exist.

The range in the average function needs to adjust to ultimately average 30 valid days.

Any ideas?

Thanks, Tony.

I've attached a sample file.

I am calculating the 30 day rolling average of mercury emissions in a power plant. If the power plant is not generating that day, the mercury number can be ignored. The average needs to then find the last valid 30 days and return that average. Example 30 day rolling avg.xlsx

Let me know if you need more information.