When did contemporary art start?

When did contemporary art start?
Sorry, but the term "contemporary" art isn't a movement in art. That means contemporary art of the 1920s is art that was in the process of being created during the 1920s, and contemporary art of today is art that is being created today. To answer your question literally, contemporary art starts now. But I think you may mean when did the idea of modern art come into play. I would say the 1950s are the start of what we call modern art and that it turned into modern art in roughly the 1970s.