Mega Backdoor Roth: How to Save $69K+ in Your 401(k) in 2024

How the Mega Backdoor Roth Works

The mega backdoor Roth involves three steps. First, you make after-tax contributions to your 401(k) plan beyond the $23,000 (2024) pre-tax or Roth 401(k) elective deferral limit. These after-tax contributions are not the same as Roth 401(k) contributions — they are a separate category that exists in many 401(k) plans. Second, you convert those after-tax contributions to Roth — either through an in-plan Roth conversion (converting after-tax money to Roth 401(k) within the plan) or an in-service distribution to a Roth IRA (rolling the after-tax money to an external Roth IRA). Third, the converted amount grows tax-free, with no further tax due on withdrawals in retirement. The key to the strategy: after-tax contributions are made with money already taxed (no upfront tax deduction), but the earnings on after-tax contributions grow tax-free once converted to Roth. The total limit for all contributions (pre-tax, Roth, after-tax, and employer match) is $69,000 in 2024 ($76,500 for age 50+). Learn how Roth conversions work →

Real-world example: Sarah, age 35, earns $200,000/year. Her 401(k) allows after-tax contributions and in-plan Roth conversions. She maxes out pre-tax contributions ($23,000) and receives a 5% employer match ($10,000). She then contributes an additional $36,000 in after-tax contributions and converts them to Roth via an automatic in-plan Roth conversion. Total 401(k) savings: $23,000 + $10,000 + $36,000 = $69,000. At 8% annual returns, her Roth account grows to approximately $3.2 million tax-free by age 65.

Which 401(k) Plans Allow the Mega Backdoor Roth

Not all 401(k) plans support the mega backdoor Roth. The plan must allow after-tax contributions (not all do — many plans only offer pre-tax and Roth 401(k) contributions). The plan must also allow either in-plan Roth conversions of after-tax money or in-service distributions of after-tax money to a Roth IRA. Plans that do not provide this feature prevent the mega backdoor Roth. Larger employers and those with more sophisticated plan administrators (Fidelity, Vanguard, Schwab) are more likely to offer these features. You can ask your plan administrator three questions: (1) Does the plan allow after-tax contributions? (2) Does the plan allow in-plan Roth conversions of after-tax money? (3) Does the plan allow in-service distributions of after-tax money to a Roth IRA? If the answer to any of these is yes, you can likely execute the mega backdoor Roth. Some plans offer automatic conversion of after-tax contributions to Roth (auto-conversion), which simplifies the process. Even if the plan does not allow after-tax contributions, you may still be able to achieve a similar result through other strategies, but none are as effective.

Tax Implications of After-Tax 401(k) Contributions

The mega backdoor Roth involves careful tax tracking. After-tax 401(k) contributions are made with after-tax dollars — they receive no tax deduction. The contribution amount itself is not taxed when converted to Roth (you already paid tax on it). However, any earnings on the after-tax contributions before conversion are taxable as ordinary income when converted. If you contribute $10,000 in after-tax money and it grows to $10,500 before conversion, the $500 gain is taxable as ordinary income. This is why it is best to convert after-tax contributions as quickly as possible — ideally within days or weeks of contribution — to minimize taxable earnings. Many plans offer automatic daily or weekly conversion of after-tax contributions, eliminating this issue. The Roth IRA five-year rule applies to the converted amounts: the converted portion of a Roth IRA cannot be withdrawn tax-free until five years after the conversion. However, this is generally not an issue for retirement savers who will not need the money until age 59.5. Learn about the Roth conversion ladder →

Mega Backdoor Roth vs. Standard 401(k) and Roth IRA

The mega backdoor Roth offers several advantages over standard retirement accounts. Compared to a standard pre-tax 401(k): you pay tax now on contributions but all future growth is tax-free (vs. tax-deferred). Compared to a Roth IRA: the contribution limit is much higher ($69,000 vs. $7,000) and there is no income limit (Roth IRAs phase out at $161,000 for single filers in 2024 — the mega backdoor Roth has no income limit for after-tax contributions). Compared to a taxable brokerage account: the mega backdoor Roth offers tax-free growth and tax-free withdrawals, while taxable accounts generate annual dividend taxes and capital gains taxes. The main disadvantage: the mega backdoor Roth requires the money to remain in the Roth account until retirement to avoid penalties and taxes on earnings. If you need the money before retirement, the standard 401(k) or taxable account may be more accessible. For most high earners who have maxed out their standard retirement accounts, the mega backdoor Roth is the best available option for additional tax-advantaged savings.

What is the mega backdoor Roth strategy?

The mega backdoor Roth is a strategy that uses after-tax 401(k) contributions combined with Roth conversions to get far more money into a Roth account than the standard contribution limits allow. The standard 401(k) elective deferral limit is $23,000 (2024) for pre-tax or Roth contributions. The mega backdoor Roth allows total contributions of up to $69,000 (2024) — the total 401(k) contribution limit that includes employer contributions, pre-tax, Roth, and after-tax contributions. The strategy works by: (1) making non-deductible after-tax contributions to your 401(k) beyond the $23,000 limit, (2) converting those after-tax contributions to Roth either within the plan (in-plan Roth conversion) or by rolling to a Roth IRA (in-service rollover). The result is that $46,000+ per year above the standard limit ends up in a Roth account, growing tax-free for retirement. The strategy requires a 401(k) plan that allows after-tax contributions and allows either in-plan Roth conversions or in-service distributions of after-tax money. Learn about Solo 401(k) plans →

Which 401(k) plans support the mega backdoor Roth?

Plans that support the mega backdoor Roth must offer two features: (1) after-tax contribution capability, and (2) either in-plan Roth conversions or in-service rollovers of after-tax money. Plans administered by major providers (Fidelity, Vanguard, Schwab, Empower) are more likely to offer these features. Among employers, large companies with sophisticated benefits packages (technology firms, financial services, consulting, law firms) are the most common providers of mega backdoor Roth capability. Small businesses with Safe Harbor 401(k) plans through providers like Vanguard or Fidelity often support after-tax contributions. Solo 401(k) plans can also support the mega backdoor Roth — self-employed individuals can often set up the right plan structure. If your employer does not support after-tax contributions, you can request that they add the feature. Many plan administrators offer after-tax contribution capability as an add-on that employers simply need to elect. There is no cost to the employer to add this feature. If the plan does not offer after-tax contributions, the mega backdoor Roth is not available through that plan. Compare 401(k), IRA, and Roth IRA →

How much can I contribute to a mega backdoor Roth in 2024?

The maximum total contribution to all 401(k) accounts (including employer contributions) in 2024 is $69,000 (or $76,500 if age 50 or older). This total includes: your pre-tax contributions (up to $23,000), your Roth 401(k) contributions (up to $23,000, combined with pre-tax), employer matching and profit-sharing contributions, and after-tax contributions. The mega backdoor Roth uses the after-tax space after other contributions are accounted for. If you contribute the full $23,000 pre-tax and receive a $10,000 employer match, you have $36,000 remaining of the $69,000 limit for after-tax contributions ($69,000 - $23,000 - $10,000 = $36,000). If your employer does not match, you could contribute up to $46,000 after-tax ($69,000 - $23,000). The limit is per person, not per plan — if you have multiple 401(k) plans (rare), the $69,000 limit applies across all plans. The limit is also per employer for controlled groups. The $69,000 limit is indexed for inflation and typically increases by $500-$1,000 per year. Learn how to manage your tax brackets →

What is the difference between a backdoor Roth IRA and a mega backdoor Roth?

The backdoor Roth IRA uses a different mechanism for a different account type. The regular backdoor Roth IRA allows high earners to contribute to a Roth IRA by making a non-deductible traditional IRA contribution and immediately converting to Roth IRA, circumventing the Roth IRA income limits. The limit is $7,000 per year (2024). The mega backdoor Roth operates through a 401(k) plan with a limit of $69,000 per year (2024). Both strategies achieve the same result — tax-free growth in a Roth account — but the mega backdoor Roth allows much larger contributions. They are not mutually exclusive: you can do both the backdoor Roth IRA ($7,000) and the mega backdoor Roth (up to $46,000+ after-tax) in the same year, for total Roth contributions of $53,000+. The regular backdoor Roth IRA is available to anyone regardless of employer plan. The mega backdoor Roth requires an employer 401(k) with specific features. High earners who have access to both should consider using both strategies to maximize their Roth savings. Learn about the backdoor Roth IRA →

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