The solution will depends on how your data looks like, if you can provide a sample workbook will be easier.
otherwise, you probably can try something like
if datetrunc('month',[your date field]) > datetrunc('month',today()) then
[your forecast value]
Thanks for the quick answer. That looks like it can work. Problem is, I get an error message from Tableau saying "Cannot mix aggregate and non-aggregate comparisions or results in 'IF' expressions". Could it be that it has something to do that my date field contains date values and my forcecast value (which is a calculated field) is a measure?
Could be. Not sure how you calculate the forecast value in your case.
It will be easier if you can share a sample workbook with the issue you mentioned.
Unfortunately the workbook contains sensitive customer data. I have something that semi-works. If I enter the formule:
"IF [Vale actual] > 0 THEN [Value Forcast] =0 END"
This gives me a T/F field that only shows the future forcecast values, which is good. But because its a filter, it filters out all the actual values. Do you might have an idea for that?
It is not necessary to be your real data, some make up data but can reflect your issue.