How to calc accumulate rate in a script logic?

Hi experts,

We are trying to generate a monthly accumulate rate in a script logic. We have a Unit rate in 12 months and we want UnitAccum rate (like YTD) in the same 12 months

Finally, we need to use this new rate in a multiplication.

How can we do it with a script logic? Any idea out there?

Kind regards

Albert Mas