1. Employee vs. Employer Contributions
Most 401(k) accounts contain both employee contributions (money the participant themselves put in) and employer match contributions. In some cases, only the employee contributions are fully vested. This distinction is critical. If the employer contributions aren’t vested, the alternate payee (usually the former spouse) may not be entitled to them or may lose a portion over time.
For example, if the employer uses a five-year graded vesting schedule, and the participant has only worked there for three years, they may only be 60% vested in employer contributions. Your QDRO must clarify what the alternate payee’s rights are if the participant quits or is terminated before fully vesting.

