How to pull info from following month, for each month

Question

I am having trouble with a task in Tableau. I need to pull in a value for each month, but the value originates in the following month (month + 1). For example, in January, I need to pull a beginning value from February, and then in February I need to pull a beginning value from March. The idea is to take the beginning value from the following month to calculate the difference from the ending value from the current month. The data I have is snapshot based, so there is one column which is the Date column, which can be 1/1/2020, or 2/1/2020 etc. (its done by month, not days).

My instinct is to create a calculated field and say something along the lines of 'where snapshot = snapshot (current) + 1 month, take in this value' but that does not work because they are not equal. I need to create a separate column or LOD for the future month I think? or a parameter?

ex. {fixed [date], [ID]: SUM( [Date] = Dateadd('month',1,[Date]) Then [Begin Value] End)}

Answer 1

I found the answer. I needed to use the LOOKUP() function.