The schedule according to which an employee of a company acquires the right to receive employer-sponsored benefits, such as payments from a pension fund, profit-sharing plan, or other qualified plan or trust, based on length of service with the company. Under the Tax Reform Act of 1986, employees must generally be vested 100% after five years of service or at 20% a year starting in the third year of service and becoming 100% vested after seven years.