The last eruption was 640,000 years ago. The eruptions seem to occur about every 680,000 years, give or take. So Yellowstone is about due.
I remember the above stat from when I read Bill Bryson’s “A Short History Of Nearly Everything” (a most excellent book btw).
According to SciGuy, just after Christmas there was a flurry of earthquakes beneath Yellowstone Lake. Could this be the big one?
If so, and you live in the US, I hope you’re on one of the coasts, as this map estimates the ash beds for the last three major eruptions: