I was granted refugee status in September 2011, and got my green card in March 2012. So I am confused by when should I have to apply for the US Citizenship. I heard regarding my case, 1. I can apply after 4 years. So 4 years from my refugee approval (2011+4) or from the green card (2012+4)? 2. I heard I can even apply 3 to 6 months early is true?

Please advise. Thanks a lot

Do you want to know when you have to apply for citizenship, or when you may apply?

I don't believe you ever have to apply.

"A lawful permanent resident can apply for United States citizenship, or naturalization, after five years of residency. This period is shortened to three years if married to a U.S. citizen. Lawful Permanent Residents may submit their applications for naturalization as early as 90 days before meeting the residency requirement.. . (emphasis added)"
https://en.wikipedia.org/wiki/Perman...United_States)

So, it appears, you may apply approximately in September of 2015 (or before now if you are married to a US Citizen), and can actually be naturalized about nine months later (or possibly earlier, if you are a spouse of a citizen).