Merge not pulling through correct information

Hi, Krisso1975 

Based on your description, I assume that you want to create a custom column based on date column. I created data to reproduce your scenario. The pbix file is attached in the end.

Table:

You may create a custom column with the following m codes.

let 
start = Date.AddDays( Date.EndOfMonth( Date.AddMonths([Date],-1)),1),
end = Date.EndOfMonth([Date]),
today = Date.From(DateTime.LocalNow())
in 
if today<start
then "Next"
else if today>end 
then "Previous"
else if today>=start and today<=end 
then "Current"
else null

Result:

Best Regards

Allan

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