Maybe you can use Index() function as a filter
Is filtering out the month all together until it is finished an option?
If it is you could make a calculated field to use as a filter.
if DATETRUNC('month', [Date field]) = DATETRUNC('month', today()) then "Exclude" else "Include" end
Then set that as a filter to exclude "Exclude".
Thanks, this worked. However, I want this calculated field to only operate on one of the series, not both. Attached is a workbook that replicates my problem. The "Exclude Incomplete Month" calculated field contains the solution you provided. Is there a way to have this filter operate on the line (3-month moving sum) and not on the bars (monthly sums)? I tried creating a parameter as present here https://community.tableau.com/message/263389#263389 but had limited success
Thanks again for all the help.