The company I work at also has 401(k) contributions vesting at 3 years. In my mental accounting I basically see this as a retention bonus - if I stick around f

The company I work at also has 401(k) contributions vesting at 3 years. In my mental accounting I basically see this as a retention bonus - if I stick around for three years they'll pay me a bonus of roughly 15% of a year's salary. As far as I know there's no tendency to fire just before vesting. But it wouldn't surprise me if you see less employees quitting between 30 and 36 months after hire, and more quitting between 36 and 42, than you would otherwise.