Buddhism is a introspection based religion and Atheism is not. It is religion in a sense of a particular system of faith in Buddha's teachings whereas Atheism has nothing specific outside of the concept of there being no god. read more
Atheism is not a religion. It's disbelief in God. In atheism,there are no pre-defined principles that one has to follow to call themselves an 'atheist' unlike Buddhism which doesn't preach the existence of God though, but it propogates the teachings and ideals of the budha after he attained enlightenment. read more
In other words, God is unnecessary in Buddhism, as this is a practical religion and philosophy that emphasizes practical results over faith in beliefs or deities. For this reason, Buddhism is more accurately called nontheistic rather than atheistic. read more