Yellowstone is not overdue for an eruption. Volcanoes do not work in predictable ways and their eruptions do not follow predictable schedules. Even so, the math doesn’t work out for the volcano to be “overdue” for an eruption. In terms of large explosions, Yellowstone has experienced three at 2.08, 1.3, and 0.631 million years ago. This comes out to an average of about 725,000 years between eruptions. That being the case, there is still about 100,000 years to go, but this is based on the average of just two time intervals between the eruptions, which is meaningless.
Most volcanic systems that have a supereruption do not have them multiple times. When supereruptions do occur more than once in a volcanic system, they are not evenly spaced in time.
Although another catastrophic eruption at Yellowstone is possible, scientists are not convinced that one will ever happen. The rhyolite magma chamber beneath Yellowstone is only 5-15% molten (the rest is solidified but still hot), so it is unclear if there is even enough magma beneath the caldera to feed an eruption.
If Yellowstone does erupt again, it need not be a large eruption. The most recent volcanic eruption at Yellowstone was a lava flow that occurred 70,000 years ago.
Learn more: Yellowstone Volcano Observatory