Say it takes five years to get fully vested. Each year, a larger portion of the company contribution is yours until the 5 years mark, then it's all yours. That the way it works at my company. I was three years vested at my last company. I left and came back. I had $20,000 vested balance but a total balance of 35K. After one year back (4 total), I got a lump sum contribution of about $7k. The next year, when I became fully vested, I got the rest. Basically, each year you get to keep another 20% of the company contribtion.