Calculator
Mega backdoor Roth calculator
Enter what you and your employer put into the plan this year; the result is the after-tax space left under section 415(c).
2026 after-tax room (mega backdoor Roth)$38,500inside the $72,000 section 415(c) limit
| Section 415(c) annual additions limit | $72,000 |
|---|---|
| Your pre-tax or Roth deferrals | −$24,500 |
| Employer match and profit sharing | −$9,000 |
| After-tax contributions possible | $38,500 |
| Total possible this year | $72,000 |
The mega backdoor works only if your plan accepts after-tax (non-Roth) contributions and allows in-plan Roth conversions or in-service withdrawals. Plans often cap after-tax contributions as a percentage of pay, and nondiscrimination testing can limit highly compensated employees.
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How the mega backdoor Roth limit works
The mega backdoor Roth limit is the section 415(c) annual additions limit, $72,000 for 2026, minus everything else that goes into your account that year: your pre-tax and Roth deferrals and your employer's match or profit sharing[n2567][k401lim]. What is left can go in as after-tax (non-Roth) contributions, and then be converted to Roth inside the plan or rolled out to a Roth IRA.
| Limit | 2025 | 2026 | 2027 |
|---|---|---|---|
| Annual additions limit (415(c)) | $70,000 | $72,000 | $75,000 |
| Employee deferral limit | $23,500 | $24,500 | $25,500 |
| After-tax room, no employer money | $46,500 | $47,500 | $49,500 |
| Catch-up on top, age 50+ | $7,500 | $8,000 | $8,500 |
| Catch-up on top, age 60–63 | $11,250 | $11,250 | $11,750 |
Catch-up contributions are not part of the 415(c) limit, so someone over 50 can add them on top[k401lim]. The limit is also capped at 100% of your pay from that employer, which matters only for low earners. The 2027 figures come from Notice 2026-66[n2667].
Worked example: $150,000 salary with a 6% match
- 2026 annual additions limit: $72,000.
- Minus your deferrals: $24,500. Minus the employer's 6% match: 6% × $150,000 = $9,000.
- After-tax room: $72,000 − $24,500 − $9,000 = $38,500, about $1,481 per biweekly paycheck.
- At 61 the same person could add the $11,250 catch-up, for $83,250 in total, the most a 60–63-year-old can put into one employer's plan in 2026.
In 2027, with the same pay and match, the room grows to $40,500.
What your plan must allow
The mega backdoor only works when the plan document has two features:
- After-tax contributions separate from Roth deferrals. Many plans don't offer them, and those that do often cap them as a percentage of pay.
- A way to get the money into Roth: an in-plan Roth rollover (conversion inside the plan)[droth], or in-service withdrawals of after-tax money that you roll to a Roth IRA. When after-tax money and its earnings come out together, IRS Notice 2014-54 lets you send the after-tax basis to a Roth IRA and the pre-tax earnings to a traditional IRA[n1454].
Earnings on after-tax money are taxable when converted, so the sooner the money moves to Roth, the less tax there is. Highly compensated employees can also be limited by the plan's nondiscrimination test for after-tax and matching contributions.
Common mistakes with the mega backdoor Roth
- Confusing after-tax with Roth deferrals. Roth 401(k) deferrals count toward the $24,500 limit; after-tax contributions are a separate source that only counts toward $72,000.
- Forgetting the employer's true-up or profit sharing. A year-end employer contribution can push the total over 415(c); plans usually stop after-tax contributions to prevent that.
- Adding plans at two employers together. The 415(c) limit applies per unrelated employer, while the $24,500 deferral limit is per person.
- Mixing it up with the IRA backdoor. The ordinary backdoor Roth uses a $7,500 IRA contribution; see Roth IRA income limits.
Related limitsYour regular deferral limits are on the 401(k) contribution limit page, and every other account is in the 2026 contribution limits table. The Roth IRA calculator shows what tax-free money grows to.
Frequently asked questions
What is the mega backdoor Roth limit for 2026?
Up to $47,500 if you defer the full $24,500 and get no employer contributions. In general it is $72,000 minus your deferrals minus employer contributions, and your plan may set a lower cap.
What is the mega backdoor Roth limit for 2027?
The 415(c) limit rises to $75,000 and the deferral limit to $25,500, so the most after-tax room with no employer money is $49,500.
Do catch-up contributions reduce the mega backdoor Roth room?
No. Catch-ups ($8,000 at 50+ or $11,250 at 60–63 in 2026) sit outside the $72,000 limit.
Is there an income limit for the mega backdoor Roth?
No income limit applies to after-tax 401(k) contributions or in-plan Roth conversions. The practical limits are your plan's rules and nondiscrimination testing.
Sources
- Notice 2025-67, 2026 Amounts Relating to Retirement Plans and IRAs
- Notice 2026-66, 2027 Amounts Relating to Retirement Plans and IRAs, as Adjusted for Changes in Cost-of-Living
- Retirement topics: 401(k) and profit-sharing plan contribution limits
- Retirement topics: Designated Roth account (in-plan Roth rollovers)
- Notice 2014-54, Guidance on Allocation of After-Tax Amounts to Rollovers