Month to Month calculation problem

Hello all

Got stuck on a problem. After some initial processing, my data now looks like this:

Now comes my issue. I need to calculate the percentage change from January to February, from Feb to March and so on.

I can obviously do the calcs with the Math Formula node, but I need to make it work all year long, and those months don’t exist yet.

Sample of math formula output:

The formula is a simple Perc calc:

Any help in solving this is greatly appreciated, currently drawing a massive blank.

Tried Transposing, Unpivoting, Multi column Math … I couldn’t make any of them do what I need.

Thanks.