I have five kids all five were conceived during a single act. Pulling out is the only form of birth control my partners and I have ever practised. in my opinion even for a very fertile person if you ( and I’m not sure how someone could fuck this up ) actually pull out there will be no conception.
This Planned Parenthood link says in theory 96% effective, in reality 78% effective. (Caveat: their definition of "effective" is not quite clear.)
https://www.plannedparenthood.org/learn/birth-control/withdr...