The process by which employees accrue non-forfeitable rights over employer contributions that are made to the employee's qualified retirement plan account. Taobiz explains Vesting Generally, non-forfeitable rights accrue based on the number of years of service performed by the employee. The exact requirements are specified in the plan document, which also contains any applicable regulations. Employees are always 100% vested in salary-deferral contributions as well as SEP and SIMPLE employer contributions.