The greatest chance so far, according to astronomers, of a large asteroid colliding with the earth and wiping life out is in 2029. Asteroids have hit the planet before, and caused mass extinctions, so there is some precedent for it happening again.
The culprit this time is the Apophis Asteroid (99942 Apophis), which is headed our way in 2029. There’s a little less than a 3% chance that this bad boy will crash into terra firma. Let’s hope Apophis gives the planet a miss, otherwise you can stop paying into your retirement account right now.