Subtract data at Different Category between 2 years

Hi,

We have data at Category ESTIMATE[2018_19] and data at CATEGORY Budget[2019_20].

I have to calculate Variance in between them i.e. Data at Budget,2020.03-Data at Estimate,2019.03 etc. I will have to do this calculation for 5 months.

I tried writing a member formula but I am not aware how to fetch Time period at run time.

Should I write a logic script for this ? If I am writing a logic Script how should I do the subtraction between two data combination ? The below script gave me error.
Please help.
Regards,

Neha

I tried it in *REC((FACTOR=1,APL_TIME=%APL_TIME_SET%,CATEGORY=BUDGET)-(FACTOR=1,APL_TIME.TMVL(-12,%APL_TIME_SET%),CATEGORY=ESTIMATE))