Mega Backdoor Roth
Calculator 2026
Calculate your annual Mega Backdoor Roth capacity inside your employer 401(k) plan. 2026 §415(c) total cap $72,000 (under 50) minus elective deferral and employer match equals after-tax bucket available for Roth conversion.
Read the full answer — method, rates and figures
Quick answer: Mega Backdoor Roth uses the §415(c) total annual additions cap ($72,000 in 2026 for under-50, $80,000 if 50+, $83,250 SECURE 2.0 super catch-up 60-63) inside an employer 401(k) plan. After subtracting the $24,500 elective deferral and employer match, the remaining bucket can be filled with after-tax employee contributions.
An in-plan Roth conversion or in-service distribution to a Roth IRA moves that money to a Roth wrapper. Convert immediately to minimize taxable earnings.
Requires plan support (only ~40-50% of plans). Compared to the regular Backdoor Roth IRA ($7,500/$8,600 annual cap), Mega Backdoor allows $30,000-$47,000 of additional Roth contributions per year.
Source: IRC §415(c), §402(g), Notice 2014-54.
Under 50
Capped at §402(g) limit $24,500
Capacity $35,500 — fill at $35,500
After-Tax Capacity
$35,500
per year available
Annual Conversion
$35,500
100% of capacity
Roth Value in 25y
$192,674
tax-free at withdrawal
Advantage vs Taxable
$31,435
vs 20% LTCG-dragged
Capacity breakdown
- • §415(c) total annual additions cap: $72,000
- • Less elective deferral (15.0% of $200,000, capped at §402(g) $24,500): $24,500
- • Less employer match (6.0% of $200,000): $12,000
- • After-tax bucket available: $35,500
- • Stack with regular Backdoor Roth IRA ($7,500 cap) = total Roth dollars per year: $43,000
⚠ Requires employer plan to permit (a) after-tax contributions beyond $24,500, AND (b) in-plan Roth conversion OR in-service distribution to Roth IRA. Read your SPD. Convert immediately each pay cycle to minimize taxable earnings on the after-tax balance.
You could put another $35,500/year into Roth.
Potential Roth value in 25 years: $192,674 — a $31,435 tax advantage over the same money in a taxable account.
But does your 401(k) actually support it?
Richify can look at your 401(k), employer match, Roth, IRA and investments together to show how much tax-advantaged space you're actually leaving unused — and whether the mega backdoor is your best next dollar.
Related: 401(k) calculator · Roth vs Traditional · Net worth calculator
Last reviewed 19 September 2026 by the Richify AI agent team.
Reviewed by Felix, Richify's AI CFO — an AI author, presented as one.
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The Mega Backdoor Roth uses your employer 401(k) plan to convert tens of thousands of additional dollars per year into tax-free Roth growth. Three mechanics make it work:
- §415(c) total cap — IRS allows total annual additions to a 401(k) up to $72,000 in 2026 (under 50). This is far more than the $24,500 elective deferral limit.
- After-tax bucket — the gap between $24,500 (elective deferral) + employer match and $72,000 (total cap) can be filled with AFTER-TAX (non-Roth) employee contributions. Capacity is typically $30,000-$47,000/year.
- Roth conversion — either in-plan Roth conversion or in-service distribution to a Roth IRA moves the after-tax money into Roth wrapper. Done quickly (same payroll), conversion is nearly tax-free.
- Plan support required — only ~40-50% of 401(k) plans permit after-tax contributions + Roth conversion. Large tech / finance employers usually do; smaller employer plans usually do not.
Source: IRC §415(c), §402(g), §72(d), Treas. Reg. §1.401-1, Notice 2014-54 (governing tax-free after-tax to Roth conversions). 2026 limits from IRS Notice N-25-67.
How much can you actually put in? The capacity formula
After-tax capacity = §415(c) total cap − your elective deferral − employer contributions. For 2026 that is $72,000 (under 50) less your deferral of up to $24,500 less whatever your employer puts in — so the theoretical maximum is $47,500, and every dollar of employer match reduces it.
A worked example. On a $200,000 salary, maxing the deferral at $24,500 with a 6% employer match of $12,000: $72,000 − $24,500 − $12,000 = $35,500 of after-tax room. Add a $10,000 profit-share and it falls to $25,500. This is the step most estimates skip — the headline “$47,500” assumes no employer contribution at all, which is rare.
The caps rise with age: §415(c) is $80,000 at 50–59 (with the $8,000 catch-up) and $83,250 at 60–63 under the SECURE 2.0 super catch-up, against elective deferral limits of $32,500 and $35,750 respectively.
The two plan features without which none of this works
This is the first thing to check, because most 401(k) plans fail at least one of them and no amount of capacity helps if the plan will not permit the mechanics:
- After-tax (non-Roth) contributions beyond the elective deferral limit. Distinct from Roth deferrals — a plan can offer a Roth 401(k) and still not allow after-tax contributions.
- Either in-plan Roth conversion or in-service distribution, so the after-tax money can move into a Roth wrapper. Without this the contributions sit as after-tax dollars earning taxable growth, which is worse than a brokerage account for most people.
Both are answered in your Summary Plan Description. Convert promptly after contributing: any growth between contribution and conversion is taxable at conversion, so the delay is what costs you.
2026 IRS limits verified 29 August 2026. Education only, not tax advice — confirm your plan's provisions and your own position with your plan administrator or a CPA.
How to use this calculator
- Verify your employer 401(k) plan permits BOTH (a) after-tax contributions beyond the $24,500 elective deferral limit AND (b) either in-plan Roth conversions or in-service distributions. Read your Summary Plan Description (SPD) or ask HR.
- Enter your salary, current pre-tax/Roth 401(k) deferral, employer match percentage, and age. The calculator computes your Mega Backdoor after-tax bucket capacity as: §415(c) total cap − elective deferral − employer match.
- Specify how aggressively you'll use the after-tax bucket (0-100% of available capacity). The calculator projects 30-year Roth growth on the converted amount at your assumed return.
- Compare against the same dollars left in a taxable brokerage account with 20% LTCG drag at withdrawal. The Mega Backdoor advantage compounds dramatically over 20-30 years.
- Stack with regular Backdoor Roth IRA ($7,500 / $8,600 if 50+) for an additional Roth bucket — many high earners do both annually for ~$42-54k total Roth dollars per year.
❓ Frequently Asked Questions
What is the Mega Backdoor Roth?
A strategy that uses your employer 401(k) plan to put up to ~$47,000 (in 2026) of after-tax contributions into the plan beyond the normal $24,500 elective deferral limit, then immediately convert that after-tax money to a Roth IRA (or Roth 401(k)) — turning what would have been a low-growth taxable bucket into tax-free Roth growth. Mechanic: §402(g) elective deferral cap is $24,500, but the §415(c) total annual additions cap is $72,000 (2026, under 50).
The space between (after subtracting employer match) is available for after-tax contributions. Then either an in-plan Roth conversion or in-service distribution to a Roth IRA moves that after-tax money into Roth wrapper.
The 'mega' prefix distinguishes from the regular Backdoor Roth IRA ($7,500 IRA cap), which is much smaller.
What does my 401(k) plan need to allow?
Two requirements: (1) The plan document must explicitly permit AFTER-TAX (non-Roth) employee contributions beyond the $24,500 elective deferral cap. Only ~40-50% of plans offer this — large tech and finance employers (Google, Meta, Microsoft, JPMC) typically do; small employer plans usually don't. (2) The plan must permit EITHER (a) in-plan Roth conversion of after-tax contributions, OR (b) in-service distribution / withdrawal of after-tax contributions while employed (so you can roll them to a Roth IRA).
Without one of these, after-tax contributions sit in a taxable bucket inside the 401(k) and the strategy fails. Read your Summary Plan Description (SPD) or ask HR.
The terms 'in-plan Roth rollover,' 'after-tax contributions,' and 'in-service distribution' should appear.
What are the 2026 contribution limits?
2026 IRS limits (Notice N-25-67) — §415(c) total annual additions cap: $72,000 (under 50), $80,000 (age 50-59 with $8,000 catch-up), $83,250 (age 60-63 with SECURE Act 2.0 super catch-up of $11,250). §402(g) elective deferral limit: $24,500 (under 50), $32,500 (50+). After-tax bucket available = total cap − elective deferral − employer match − any other §415(c) additions.
Example: $200k salary, max elective deferral $24,500, 6% employer match = $12,000. After-tax bucket available = $72,000 − $24,500 − $12,000 = $35,500 (under 50).
This $35,500 is the Mega Backdoor capacity for that year.
Should I do in-plan Roth conversion or in-service rollover?
Depends on what your plan allows and your preference. (a) In-plan Roth conversion: convert the after-tax 401(k) money to a Roth 401(k) sub-account within the same plan. Pros: simple, automatic via plan administrator.
Cons: subject to plan rules (e.g., investment options, fees), money stays in 401(k) until separation/distribution. (b) In-service rollover to Roth IRA: distribute the after-tax money and roll to an external Roth IRA. Pros: full investment freedom (any IRA-eligible holdings), avoids future 401(k)→IRA rollover at separation, withdrawal flexibility.
Cons: requires more steps each year. Either way the conversion is generally tax-free IF you act quickly — any earnings on the after-tax contributions between deposit and conversion ARE taxable.
Many practitioners convert immediately (same payroll cycle or weekly) to minimize taxable earnings.
What's the difference between Mega Backdoor Roth and regular Backdoor Roth?
Different vehicles, very different scale. REGULAR Backdoor Roth: uses Traditional IRA.
Annual cap $7,500 ($8,600 if 50+). Pro-rata rule under §408(d)(2) makes it complicated if you have pre-tax IRA balances.
Conversion is generally tax-free if no pre-tax IRA. MEGA Backdoor Roth: uses employer 401(k).
Annual capacity up to ~$47,000+ depending on salary and employer match. No pro-rata complication (401(k)/IRA aggregation rules differ).
Requires employer plan support. Many high earners do BOTH each year — $7,500 regular Backdoor + ~$35-47,000 Mega = $42-54,000 into Roth annually.
Combined with regular Roth 401(k) ($24,500 elective deferral) total Roth-bucket dollars per year can exceed $70,000.
What is the pro-rata rule for Mega Backdoor Roth?
Different from the IRA pro-rata rule. For 401(k) after-tax conversions, the IRS does a separate pro-rata calculation between (a) the after-tax CONTRIBUTIONS (your basis — should be tax-free on conversion), and (b) the EARNINGS on those after-tax contributions while sitting in the 401(k) (taxable on conversion).
If you convert weekly/same-pay-cycle, earnings are near-zero so the conversion is nearly tax-free. If you wait years to convert, accumulated earnings on the after-tax bucket become a large taxable amount.
The §72(d) ordering rule may allow some carving — your specific plan administrator handles this on Form 1099-R issuance.
Do employer matches reduce my Mega Backdoor capacity?
Yes — directly. Employer contributions (match + any non-elective contributions) count toward the §415(c) $72,000 total annual additions cap.
Example: $200k salary, you max elective deferral at $24,500, employer puts in 6% = $12,000 match, your after-tax capacity is $72,000 − $24,500 − $12,000 = $35,500. If your employer profit-shares an additional $10,000, that further reduces capacity to $25,500.
SECURE Act 2.0 allows employees to elect Roth-treatment for employer matches (Roth match), but this doesn't change the §415(c) cap — it just changes the tax characterization. Always factor in expected total employer contributions when planning your after-tax election.
Is the Mega Backdoor Roth at risk of legislative elimination?
It was proposed for elimination in the Build Back Better Act (2021) Section 138302 — which would have prohibited after-tax 401(k) contributions and conversions starting January 1, 2022 for everyone, and applied retroactively to high earners ($400k+ single / $450k MFJ) by 2031. The bill failed to pass the Senate.
As of 2026, no successor legislation has been enacted. The strategy remains legal under current Treasury regulations and the §415(c) framework.
However, future tax legislation could close the loophole — many practitioners view the strategy as moderately politically vulnerable but currently sound.
Can I do a Mega Backdoor Roth with a Solo 401(k)?
Yes, IF your Solo 401(k) provider permits after-tax contributions AND in-plan Roth conversions or in-service distributions. Most major brokerage Solo 401(k) plans (Fidelity, Schwab, Vanguard) historically did NOT support after-tax contributions — they only allowed pre-tax + Roth elective deferrals.
As of 2026, Charles Schwab, E*TRADE, and a few third-party custom Solo 401(k) providers (My Solo 401k Financial, Sense Financial, others) explicitly support the Mega Backdoor structure. Self-employed individuals with substantial business income can potentially contribute up to the full $72,000 §415(c) cap themselves (as both employee and employer of their own LLC/S-corp), making the Mega Backdoor especially powerful for high-income solopreneurs.
How fast should I convert after contributing?
As fast as possible to minimize taxable earnings. Best practice: same payroll cycle conversion.
Many plans (Google, Meta, Microsoft 401(k)) offer 'automatic in-plan conversion' that converts each after-tax contribution to Roth on the same day it's deposited — zero taxable earnings, fully tax-free conversion. If your plan requires manual conversion, do it weekly or monthly at minimum.
Quarterly or annual conversion lets earnings accumulate, increasing the taxable portion. Example: $35,000 after-tax contributions left in a 401(k) at 10% return for a year creates $3,500 of taxable earnings on conversion at your marginal bracket — at 32% bracket = $1,120 in tax that could have been zero with daily conversion.
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