1% is a Polish child learning Polish and 100% is fluent
I think it's not a good mesurement. Children learn in totally different way than adults. e.g. 2 yo kid understands almost everything his mother is saying to him while may not be able to say a word himself. On the other hand, adults usually start with translating from their mother tongue and it takes some time to switch to thinking in a new language.
If you have already learned some grammar and vocabulary you're gonna have a good oportunity to practice it 'in the filed' and you may do really big progress.
But if you're completely blank, being here may not help you at all unless you take lessons to help you to start with the basics, or have someone to talk and explain everything (like mother to her child).