There are many different forms of qualified retirement plans--among them, 401(k), profit sharing,
defined benefit, ESOPs, 403(b), SIMPLE IRAs, and SIMPLE 401(k) plans. One of the unique requirements of SIMPLE IRAs and SIMPLE 401(k) plans is that they must be the sole, exclusive plan of the employer for the entire calendar year. In other words, an employer sponsoring a SIMPLE IRA or SIMPLE 401(k) cannot, in the same calendar year, also sponsor a regular 401(k) plan or any other qualified retirement plan.
