When are you a Buddhist? I know labelling people is not in the spirit of Buddhism.  I am for example member of a Buddhist society, not because I'm so eager to be one but because in my country each religious society gets quite some money for having members (and if your not a member,  the church gets the money). 

But when do people (not born into a Buddhist country) call themselves Buddhists?
I live in a country where most people are either atheist or christian. Estimates are that between 0.4 and 1% of all people here call themselves a Buddhist.

It's been my experience that there isn't a single agreed upon definition about when you can call yourself a Buddhist. Some people say you are a Buddhist if you consider yourself to be one, others say you need at least several years training from an acknowledged Buddhist teacher. This being said, most people I know (but certainly not all) regard the ceremony of 'taking refuge' as the moment when they became a true Buddhist. 

Personally I like the view of Dzongsar Jamyang Khyentse Rinpoche who has written a book on the topic called "What Makes You Not a Buddhist":


  It’s whether you agree with the four fundamental discoveries the Buddha made under the Bodhi tree, and if you do, you can call yourself a Buddhist (source).


Disclaimer: this answer is largely based on my own answer on a similar question