The Mega Backdoor Roth and America’s Uneven Retirement Tax Code
Why Access to the Best Roth Treatment Depends on Where a Person Works
Abstract: American retirement law gives workers dramatically different opportunities to place savings in Roth accounts depending on whether their employer offers a sufficiently flexible 401(k) plan. This article explains how a high-income worker with access to the mega backdoor Roth may place as much as $72,000 into Roth status in 2026, while a similarly situated worker without a workplace plan is generally limited to a $7,500 IRA contribution. It considers reforms that would make Roth saving opportunities more portable and consistent across workers.
Two recent articles at Economic Memos identify a basic inequity in American retirement policy. The tax code does not simply encourage people to save. It gives substantially different saving opportunities to workers depending on whether they have a 401(k), what features their employer has selected, and whether they currently work for an employer that sponsors a suitable plan.
Workers with 401(k) plans generally receive much higher contribution limits than workers dependent on individual retirement accounts. They may also receive employer matching contributions, automatic enrollment, payroll deductions, and institutional investment options. Many workers who lack access to an employer-sponsored plan—particularly employees of small businesses, part-time workers, caregivers, and people moving between jobs—must rely primarily on IRAs with lower contribution limits and generally no employer match.
My earlier retirement-policy proposal therefore advocated universal automatic IRAs, higher IRA limits, and permission for employers to contribute directly to portable employee-owned accounts.
My more recent examination of whether workers should roll old 401(k) balances into IRAs uncovered additional disparities. Keeping money inside a 401(k) can preserve penalty-free access under the rule of 55, keep pretax assets outside the IRA pro-rata calculation used for backdoor Roth conversions, and preserve stronger and more uniform creditor protections. An IRA may offer lower fees and broader investment choices, but it is not a complete substitute for an employer plan.
The discussion that follows identifies three disparities in Roth retirement saving, including unequal access to the mega backdoor Roth.
The first disparity involves direct access and complexity. In 2026, eligibility to contribute directly to a Roth IRA phase out between $153,000 and $168,000 of modified adjusted gross income for single taxpayers and between $242,000 and $252,000 for married couples filing jointly. Above the applicable limit, the taxpayer cannot make a direct Roth IRA contribution.
No comparable income restriction applies to designated Roth 401(k) contributions. A worker earning $300,000, $500,000, or more may still contribute the full employee maximum to a Roth 401(k), provided the employer’s plan offers one. The Roth IRA income restrictions do not apply to designated Roth workplace contributions.
A high-income worker without a workplace plan may often use the ordinary backdoor Roth strategy, but only up to the much smaller IRA contribution limit and subject to the pro-rata rule discussed below.
The second disparity involves contribution limits. In 2026, a worker under age 50 may contribute $24,500 through regular 401(k) salary deferrals, while the total defined-contribution-plan limit—including employee contributions and employer contributions—is generally $72,000. The IRA contribution limit is only $7,500.
The third disparity is the mega backdoor Roth itself. This is not a separate account established by law for everyone. It is a strategy available only when a particular employer plan permits after-tax employee contributions beyond the normal $24,500 salary-deferral limit and permits those contributions to be moved into Roth status through an in-plan Roth conversion or qualifying rollover.
Consider two unmarried, high-income workers under age 50. Each earns $300,000 and has enough disposable income to save substantially more than the ordinary retirement limits.
Worker One: Qualifying Roth 401(k) Plan
The overall limit on annual additions to this worker’s 401(k) is the lesser of 100 percent of compensation or $72,000 in 2026.
The following cases show different ways the same $72,000 can be divided between employee and employer contributions and between Roth and conventional pretax accounts.
The examples assume that the worker is under age 50, earns at least $72,000, and has a particularly flexible 401(k) plan that permits:
Designated Roth 401(k) elective deferrals.
Voluntary employee after-tax contributions beyond the ordinary elective-deferral limit.
Prompt in-plan Roth conversions of those after-tax contributions.
In-plan Roth conversions of other eligible plan balances.
Not every plan offers these features. A plan may also restrict contributions by highly compensated employees to satisfy nondiscrimination rules. In 2026, the regular employee elective-deferral limit is $24,500, while total annual additions—including employee after-tax contributions and employer contributions—generally cannot exceed $72,000.
Case One: No Employer Contribution
Begin with the simplest case. Assume that the employer makes no matching, profit-sharing, or other contribution.
The worker contributes the entire $24,500 elective-deferral limit directly to the Roth 401(k). The worker then makes an additional $47,500 voluntary after-tax employee contribution:
Direct Roth 401(k) elective deferral: $24,500
Voluntary after-tax employee contribution: $47,500
Total annual additions: $72,000
The additional $47,500 is not another elective deferral and is not an employer contribution. The employee has already exhausted the $24,500 limit that applies collectively to regular pretax and Roth elective deferrals. The remaining contribution capacity is calculated as follows:
$72,000 overall limit − $24,500 Roth elective deferral = $47,500
The $47,500 initially enters the plan as a non-Roth after-tax employee contribution. If the plan permits a prompt in-plan Roth conversion, the worker can move it into the plan’s Roth account. Because income tax has already been paid on the contribution, generally only investment earnings accumulated before the conversion are taxable.
Under these assumptions, the worker personally contributes the entire $72,000, and the entire amount can enter Roth status.
Case Two: A $10,000 Conventional Employer Match
Now assume that the employer contributes a $10,000 conventional pretax match. The match counts toward the same $72,000 overall limit. It therefore reduces the employee’s remaining voluntary after-tax contribution capacity:
$72,000 − $24,500 Roth elective deferral − $10,000 employer match = $37,500
The annual additions would initially consist of:
Employee’s direct Roth 401(k) contribution: $24,500
Employee’s after-tax contribution converted to Roth: $37,500
Employer’s conventional pretax match: $10,000
Total annual additions: $72,000
The worker contributes $62,000, and the employer contributes $10,000. Of the worker’s contribution, $24,500 enters directly as a Roth elective deferral, while $37,500 initially enters as a non-Roth after-tax contribution.
If the plan permits a prompt in-plan Roth conversion, the worker may convert the $37,500 to Roth status. Because the worker has already paid income tax on that contribution, the conversion generally produces no additional taxable income except for any investment earnings accumulated before the conversion. If the conversion occurs promptly, those earnings—and therefore the resulting tax—may be negligible.
After the conversion, $62,000 is in Roth status, while the $10,000 employer match remains in the conventional pretax portion of the plan.
The worker could leave the employer match pretax. Alternatively, if the match is vested and the plan permits an in-plan Roth rollover, the worker could subsequently convert the $10,000 match to Roth. The previously untaxed $10,000, together with any untaxed earnings included in the conversion, would then be added to the worker’s taxable income for that year.
After that conversion, the entire $72,000 in annual additions would be held in Roth status. The conversion would not create another contribution or increase the $72,000 limit. It would merely change the tax character of the $10,000 already contributed by the employer.
Case Three: The Employer Match Is Roth From the Outset
SECURE 2.0 created another possibility. A plan may allow an employee to designate certain fully vested matching and nonelective employer contributions as designated Roth contributions when they are allocated. This option is not mandatory; the employer’s plan must affirmatively offer it.
If the plan permits the $10,000 employer match to be designated Roth from the outset, the annual additions would be:
Employee’s direct Roth 401(k) contribution: $24,500
Employee’s after-tax contribution converted to Roth: $37,500
Designated Roth employer match: $10,000
Total annual additions entering Roth status: $72,000
The same $72,000 limit applies. The difference from Case Two is the treatment of the employer contribution. Instead of first entering a conventional pretax account and possibly being converted later, the $10,000 match enters Roth status when allocated. The amount is included in the employee’s taxable income for that year.
These three cases are alternative allocations of the same annual limit:
With no employer contribution, the employee may personally contribute the entire $72,000.
With a conventional $10,000 match that remains pretax, $62,000 enters Roth status and $10,000 remains pretax.
If the conventional match is later converted, or is designated Roth when made, the entire $72,000 may ultimately enter Roth status.
Other allocations are possible. The employee could divide the $24,500 elective deferral between pretax and Roth contributions. The employer could make matching, profit-sharing, or nonelective contributions. Those employer contributions would reduce the remaining room for voluntary employee after-tax contributions because they all count toward the same $72,000 limit.
The central comparison remains striking. A high-income worker with the right employer plan may be able to place the full $72,000 in annual additions into Roth status.
Worker Two: No Workplace Retirement Plan
The second worker has no 401(k). Because the worker’s income exceeds the Roth IRA ceiling, no direct Roth IRA contribution is permitted. The worker may instead contribute $7,500 to a nondeductible traditional IRA and convert it to a Roth IRA through the ordinary backdoor Roth strategy.
But the backdoor transaction does not increase the IRA contribution limit. It merely provides an indirect route for putting the same $7,500 into Roth status.
The annual comparison is therefore:
Worker with the qualifying 401(k): $72,000 in new Roth savings
Worker limited to an IRA: $7,500 in new Roth savings
Difference: $64,500
The worker with the qualifying 401(k) can place 9.6 times as much new money into Roth accounts as the worker who relies entirely on an IRA.
Using the 2026 limits as a constant illustration and ignoring investment returns, ten years of contributions would total $720,000 for the worker with the qualifying plan, compared with $75,000 for the IRA-only worker.
The IRA-only worker’s position may be even worse if that person already holds pretax traditional, SEP, or SIMPLE IRA balances. The ordinary backdoor Roth is then subject to the IRA pro-rata rule, which can make most of the conversion taxable.
Pretax money retained in a 401(k), by contrast, is excluded from that IRA calculation—another advantage attached to workplace-plan access. A worker planning regular backdoor Roth conversions should therefore consider the pro-rata consequences before rolling pretax 401(k) assets into an IRA. This was explained in my memo on rollovers from 401(k) plans to IRAs. Probably don’t do the rollover if you are planning to do backdoors through IRAs.
Congress should choose a consistent principle. It could create a portable, workplace-independent supplemental Roth account available to all workers, subject to a uniform combined contribution limit. It could permit employers to make matching contributions directly into employee-owned IRAs. Alternatively, Congress could restrict exceptionally large plan-based Roth contributions while increasing ordinary IRA limits.
Retirement policy should reward comparable saving consistently—not reserve its most valuable Roth opportunities for a select group fortunate enough to work for the right company.