Can a previous employer contribute to my closed 401k after termination

There are several reasons that money can be added after your last day of work.

• It can be money from your last paycheck.
• It can be money from the payout of vacation/sick/PTO.
• It can be money from a severance payout.
• It can be matching funds from any of these contributions.
• It can be a profit sharing payment. My employer pays the bonus to all employees who worked 1000 hours the previous year. The payment to my 401(k) is in March each year.
• It can be some other bonus.

To determine the source and if it your funds, or if it is from the company and you might be partially or 100% vested, you will need to look at the activity section of the account. Every 401K I have had tells me the source of all deposits, and the vesting status of those funds. The account balance section should also tell you if is partially or 100% vested.

I would expect that at 5 years and two months you are 100% vested, but if you had worked fewer years these funds might be only partially vested if they were from the company.

You mention that the website identifies the transaction as "employer additional". I would look back over the last few years to see if there are other deposits with the same description.

Check your termination paperwork. They should have information on the timing of them paying out your last check, PTO balance, and any severance. In some cases they give you options regarding 401(k) contributions.