Like I said above, it's three....... for now.
Here's George R R Martin's schedule on his series:
A Game of Thrones (1996)
A Clash of Kings (1998)
A Storm of Swords (2000)
A Feast for Crows (2005)
A Dance with Dragons (forthcoming) - this was meant to be the last book
The Winds of Winter (forthcoming)
A Dream of Spring (forthcoming)
It's not looking good for a finish before 2020.