Employee and Employer Contributions
One of the most important steps in dividing this 401(k) plan is identifying what portion of the balance comes from employee contributions (which are always 100% yours or your spouse’s) and what comes from employer contributions (which may be subject to vesting rules).
For example, employer contributions might only vest incrementally over several years. If your spouse has not worked long enough to be fully vested, part of the “account balance” might actually be lost if they leave their job—or after divorce. This can dramatically change how much is divisible.

