What Is a Mega Backdoor Roth? The Ultimate High-Earner Strategy
Save up to $46,000 extra per year in a Roth account—even if you earn too much for regular Roth IRA contributions.
Key Takeaways
- 1Mega backdoor Roth lets you contribute up to $69,000 total to 401k (2025)
- 2Only ~30% of 401k plans allow the after-tax contributions required
- 3You make after-tax contributions, then convert to Roth
- 4Result: Massive Roth savings beyond normal limits
- 5Must have in-plan Roth conversions or in-service distributions
- 6Powerful for high earners who max out regular retirement contributions
What Is a Mega Backdoor Roth?
The mega backdoor Roth is a strategy that lets you put significantly more money into Roth accounts:
- Regular Roth IRA limit: $7,000 (plus $1,000 catch-up if 50+)
- Mega backdoor potential: Up to $46,000 additional
- How: After-tax 401k contributions converted to Roth
- Who it's for: High earners who max out regular contributions
- Why "mega": It's much larger than regular backdoor Roth ($7k)
- Tax benefit: Decades of tax-free growth on $46k+ per year
How It Works
The mega backdoor Roth exploits a gap in 401k contribution rules:
- 1. Employee contribution limit: $23,500 (pre-tax or Roth)
- 2. Total 401k limit: $69,000 (employee + employer)
- 3. The gap: If your employer contributes $10k, you can add $35.5k after-tax
- 4. After-tax contributions are not pre-tax and not Roth—a third bucket
- 5. You then convert these after-tax dollars to Roth
- 6. Result: Up to $46,000 extra going to Roth annually
| Contribution Type | 2025 Limit | Tax Treatment |
|---|---|---|
| Pre-tax/Roth employee | $23,500 | Pre-tax or Roth |
| Employer match | Varies (counts toward $69k) | Pre-tax |
| After-tax employee | Remainder up to $69k | After-tax → convert to Roth |
| Total combined limit | $69,000 | Mixed |
Calculating Your Mega Backdoor Capacity
Your mega backdoor limit depends on employer contributions:
- Formula: $69,000 - Your contributions - Employer contributions = After-tax room
- If you max employee contributions ($23,500) and employer matches $10,000
- Your mega backdoor room: $69,000 - $23,500 - $10,000 = $35,500
- Catch-up (50+): Adds $7,500 to employee limit, making total $76,500
| Your Salary | Employer Match (6%) | Max After-Tax | Mega Backdoor Potential |
|---|---|---|---|
| $100,000 | $6,000 | $39,500 | $39,500 |
| $150,000 | $9,000 | $36,500 | $36,500 |
| $200,000 | $12,000 | $33,500 | $33,500 |
| $300,000+ | $20,700 (max) | $25,300 | $25,300 |
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Does Your 401k Plan Allow It?
Not all plans support mega backdoor Roth. You need:
- After-tax contributions allowed (only ~30% of plans)
- In-plan Roth conversions OR in-service distributions
- No limits on after-tax contribution amounts
- Ask HR: "Does our plan allow after-tax 401k contributions?"
- Ask HR: "Can we do in-plan Roth conversions?"
- Check Summary Plan Description (SPD) for details
Step-by-Step: How to Execute
If your plan allows it, here's the process:
- 1. Max out pre-tax or Roth contributions first ($23,500)
- 2. Set up after-tax contributions up to the $69k limit
- 3. Immediately convert after-tax dollars to Roth (in-plan or roll out)
- 4. The conversion should happen quickly to minimize taxable gains
- 5. Document everything for tax purposes
- 6. Repeat each pay period for dollar-cost averaging
Pro-Rata Rule Warning
If you have pre-tax after-tax dollars mixed and don't convert immediately, the pro-rata rule may apply, creating a taxable event. Convert after-tax contributions to Roth as quickly as possible—ideally each pay period.
Diversify Your Tax-Advantaged Savings
While mega backdoor Roth maximizes tax-free stock market exposure, consider diversifying into other assets too:
- Gold IRA provides different kind of diversification
- Not correlated with stocks—true hedge
- Physical gold holds value during market crashes
- Can be Traditional or Roth Gold IRA
- Balance growth assets with stability assets
Frequently Asked Questions
1Is mega backdoor Roth legal?
Yes, completely legal. It's been confirmed by IRS guidance and used by sophisticated investors for years. However, legislation has been proposed to eliminate it—take advantage while you can.
2What if my plan doesn't allow after-tax contributions?
Then mega backdoor Roth isn't available to you through this employer. You can still do regular backdoor Roth IRA ($7k). Consider asking HR if they can add after-tax contributions to the plan.
3Should I do mega backdoor Roth or regular investing?
If you can afford it and your plan allows it, mega backdoor Roth first. The tax-free growth over decades is extremely valuable. Taxable brokerage is fine, but it doesn't offer the same tax benefits.
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