Updated January 2022

Generally, there are two ways to execute the Mega Backdoor Roth Conversion:

  1. Voluntary after-tax contributions --> in-plan Roth conversion to Roth 401k

  2. Voluntary after-tax contributions --> in-service distribution to Roth IRA

In-Plan Roth Conversion: After-Tax Funds to Roth

If you are implementing a backdoor Roth conversion, you might make voluntary after-tax contributions to the Solo 401k plan and then decide to convert those funds in-plan to Roth.

Generally, converting after-tax contributions to a Roth 401k is not a taxable event. That’s because you didn’t claim a deduction on the initial contribution. Therefore, the IRS does not expect any taxes on the conversion.

The gross distribution is the amount you are converting to Roth in-plan. However, because you are converting after-tax contributions to Roth, the taxable amount in box 2a is $0. Per IRS instructions, enter the amount as -0-.

Similar to the after-tax to Roth conversion, the payer will be listed as the 401k trust and the recipient will be you as the plan participant.

Enter the amount of voluntary after-tax conversions in box 5 as the basis for your conversion. We strongly recommend completing the conversion before the after-tax funds have had any growth (this growth is taxable).

For Box 7, enter Distribution code G as this is a direct rollover inside your qualified plan. As long as there is no growth on your after-tax contributions (move contributions only), there should be no taxes owed on the in-plan Roth conversion/direct rollover.

In-Service Distribution: Move Money to a Roth IRA

Another strategy of the Mega Backdoor Roth conversion is to backdoor funds into a Roth IRA. Simply put, the Solo 401k account holder can make large voluntary after-tax contributions to the Solo 401k plan. Those contributions are then moved to a Roth IRA via an in-service distribution.

In this instance, the PAYER is the Solo 401k trust. Enter the Solo 401k trust name, Solo 401k trust EIN, and Solo 401k trust address on IRS form 1099-R.

For the RECIPIENT, enter your name, your address, and your social security number. You do not need to enter the Roth IRA custodian information.

Similar to the after-tax to Roth conversion, the taxable amount in box 2a is -0- as you are moving after-tax funds to another after-tax account.

Use Distribution Code H in box 7, which is for a Direct rollover of a designated Roth account distribution to a Roth IRA.

When to File

As the plan administrator, you need to furnish a copy of the form to yourself by February 1st. The IRS needs a copy by March 1st (if you file by mail) or March 31st (if you e-file, which is highly recommended).

Where and How to File

The IRS will not accept a paper filing of IRS form 1099-R. Only approved filers on the FIRE system may file the form. There are numerous helpful online services that will file the form for just a few dollars. Some resources include:

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