describes the collective effects of changes in the Earth's movements upon its climate[.]
By this theory, the Earth is now experiencing an interglacial.
By the theory, when will the interglacial end and the next ice age begin?
This paper seems to be discussing what you've asked: http://www.sciencemag.org/content/297/5585/1287.full. The next ice age is expected to begin about 50,000 years from now. However, I think it's still debatable how accurate the predictions of Milankovitch cycles are, and how much of an effect humans are likely to have on this earth system.