Sodium stearate - calculation

Hi !

My goal is to create lotion with NaoH /stearic acid as emulsifier.

My oil phase is:

15% mineral oil

20% isopropyl myristate

I need to calculate how much NaOH is needed to saponify 5% stearic acid.

Chemical reaction will be as follow:

C₁₇H₃₅COOH + NaOH ⇒ C₁₇H₃₅COONa + H₂O

My question is should I included saponification value for stearic acid or treat this calculation as normal proportion:

284.4772 g/mol - 40 g/mol

5% - x

Second option as I have mentioned is taking into account saponification value for stearic acid which is between 206 and 212, so let's say for calculation purpose we will take 209.

So then I would have to recount amount KOH for the NaOH.

It seems to be easy, but I think I am lost here !

Any help ?