How many stars are in the milkiway?

A good guess would be about 400 billion. However, this is ONLY a guess, since we really have no idea how common the "just barely a star"-type of red dwarf or brown dwarf stars are. For example, the CLOSEST star to our Sun is the red dwarf star Proxima Centauri. Even though it is closest, it is too dim to be seen without a telescope!