A Mega-backdoor Roth IRA is a strategy that allows high-income earners to contribute significantly more to their Roth IRA than the standard limits by leveraging after-tax contributions to a 401(k) plan.
The IRS provides guidelines on 401(k) contributions and rollovers in IRS Pub. 575, “Pension and Annuity Income” and the instructions for Form 8606. These documents outline the tax implications and reporting requirements for after-tax contributions and Roth conversions.
Here’s a detailed breakdown of the tax reporting process for this strategy:
Your after-tax contributions are included in Box 1 of your Form W-2, they do not reduce your taxable income since they are made with after-tax dollars.
If you convert after-tax contributions to a Roth 401(k) within the same plan, this is a non-taxable event since the contributions were already taxed. If you roll over after-tax contributions to a Roth IRA, you must report this on IRS Form 1099-R.
The distribution code in Box 7 of Form 1099-R will indicate the type of rollover. For a direct rollover to a Roth IRA, the code is typically “G”.
This box shows the total amount rolled over.
This box should be $0 if only after-tax contributions are rolled over. If there are earnings on the after-tax contributions, those earnings are taxable and will be reported here.
Use IRS Form 8606 to report the rollover of after-tax contributions to a Roth IRA. This form ensures that the after-tax contributions are not taxed again. Specifically, Part II of Form 8606 is used to report the conversion of after-tax amounts to a Roth IRA.