You’re Doing Catch-Up Contributions WRONG
(Roth vs Mega Backdoor Roth Explained)

If you’re a solopreneur aged 50 or older, you’ve probably heard about catch-up contributions — and you may also have heard the term Mega Backdoor Roth. But here’s the problem: many self-employed individuals confuse these two completely different strategies, or worse, assume they’re the same thing. Getting this wrong can mean leaving tens of thousands of tax-advantaged retirement dollars on the table every year. In this session of the My Solo 401k Financial daily webinar series, we break down exactly how each strategy works inside a Solo 401k plan.

What Are Catch-Up Contributions — and Who Can Make Them?

A catch-up contribution is an additional amount that workers aged 50 or older are permitted to contribute to a retirement plan each year, over and above the standard annual employee elective deferral limit. Congress created catch-up contributions specifically so older workers have a chance to accelerate their retirement savings as they approach their peak earning years.

Inside a Solo 401k, catch-up contributions are made on the employee (elective deferral) side of the plan — not on the employer profit-sharing side. For 2026, the standard employee deferral limit is $24,500. Eligible participants aged 50–59 or 64 and older may contribute an additional $8,000 in catch-up contributions, bringing their total employee deferral to $32,500. Thanks to the SECURE Act, participants aged 60–63 qualify for a higher “super catch-up” of $11,250, for a total employee deferral of $35,750.

Catch-Up Contribution Age Tiers Under the SECURE Act (2026)

Roth Catch-Up vs. Mega Backdoor Roth: The Critical Difference

This is the confusion that trips up most solopreneurs. Both strategies involve Roth dollars inside a Solo 401k, but they operate through completely different mechanisms, have different contribution sources, and unlock dramatically different dollar amounts. Understanding the distinction is essential to maximizing your retirement strategy.

Option 1: Roth Catch-Up Contributions (Employee Deferral Side)

A Roth catch-up contribution is simply designating your regular catch-up contribution — up to $8,000 or $11,250 depending on your age for 2026— as Roth (after-tax) dollars instead of pre-tax. You’re working within the same annual employee deferral cap. The money goes in after-tax directly to your Roth Solo 401k account, grows tax-free, and qualified withdrawals are tax-free in retirement.

• Source: Employee elective deferral (the same pool as your regular deferral)
• 2026 maximum catch-up amount: $8,000 (ages 50–59 / 64+) or $11,250 (ages 60–63)
• Tax treatment: After-tax going in; tax-free growth and withdrawals
• Limitation: Counts within the total employee deferral cap

Option 2: Mega Backdoor Roth — Voluntary After-Tax Contributions

The Mega Backdoor Roth strategy is an entirely separate contribution bucket. It uses the voluntary after-tax contribution feature of a Solo 401k — a feature that discount brokerage prototype plans (like Fidelity’s off-the-shelf plan) do not include but that a custom plan like the one offered by My Solo 401k Financial does. Here’s why it’s called “Mega”: the available dollar amounts are far larger than a standard Roth or Roth catch-up.

The total annual additions limit under IRC Section 415 for 2026 is $72,000 (or $80,000 / $83,250 with catch-up depending on age). This cap includes employee deferrals plus employer profit-sharing contributions plus voluntary after-tax contributions.

Side-by-Side Comparison: Roth Catch-Up vs. Mega Backdoor Roth

Key Takeaways: Stop Leaving Roth Dollars on the Table

The confusion between Roth catch-up contributions and the Mega Backdoor Roth is costing solopreneurs real money every year. Here’s what to remember:

• Catch-up contributions (Roth or pre-tax) are available to those aged 50+, within the employee deferral cap (for 2026: $8,000 for most; $11,250 for ages 60–63 per the SECURE Act).
• The Mega Backdoor Roth uses voluntary after-tax contributions to fill the space between your deferrals + profit-sharing and the full $72,000 Section 415 cap for 2026 (or some skip employee and employer make 100% voluntary after-tax contributions) — available at any age, far larger amounts. Note: Catch-up contributions are additional contributions above the overall limit
• The Mega Backdoor Roth requires a plan that explicitly allows voluntary after-tax contributions (like the plan offered by My Solo 401k Financial) — not all Solo 401k plans do.