When you feel that you can say pretty much everything you want to people naturally without getting stuck in the middle of a sentence,then you will be fluent.This can only be achieved,in my opinion,by practising every day and by surrounding yourself with English as much as you can.

There are some formal levels of language. But frankly, I think it's up to you when you're satisfied with your knowledge. Some people want just to understand their favourite series, some want to talk with native speakers. So, you have more deffinition what fluency means. I tend to think, it's up to you.