A mega backdoor Roth for doctors works only when the 401(k) allows after-tax contributions and a Roth conversion, and Assante Wealth Management starts by checking both features before payroll changes.
For 2026, $24,500 of employee deferrals plus $15,000 of employer contributions leaves $32,500 under the $72,000 defined contribution limit before catch-up contributions.
The answer can differ for two doctors with the same income. A physician with taxable cash and a stable plan may use the available room, while a practice owner reserving tuition money, sale costs, or a cash buffer may contribute less. Assante Wealth Management reviews the plan language, payroll timing, and family cash calendar together for its clients.
Step 1: Find the plan features before changing payroll
Start with the summary plan description, adoption agreement, benefits portal language, and a written answer from the plan administrator. Ask specifically whether the 401(k) accepts voluntary after-tax employee contributions and whether it permits an in-plan Roth conversion or a distribution to a Roth IRA.
A Roth 401(k) deferral is different from a voluntary after-tax contribution. The first is a designated Roth contribution subject to the employee deferral limit. The second can use room under the larger defined contribution ceiling, but only if the plan permits it.
The slip here is treating a Roth option as proof that voluntary after-tax contributions exist. They are separate features. Assante Wealth Management asks for the actual plan language before changing a physician's payroll election.
- Summary plan description
- Adoption agreement
- Benefits portal language
- Administrator's written answer
Step 2: Calculate the room under the annual ceiling
For 2026, the IRS defined contribution limit is $72,000. Subtract employee deferrals and employer contributions from that amount; catch-up contributions do not reduce the $72,000 total limit.
The employee deferral limit is $24,500, or $32,500 with the $8,000 catch-up for someone age 50 or older. At ages 60 through 63 the catch-up rises to $11,250. Under IRS rules, a doctor whose prior-year FICA wages exceeded $150,000 has to make any catch-up as a Roth contribution.
Kwame needs separate records for his practice plan and the hospital system's plan if a possible sale changes his employment or participation. A payroll screen showing $24,500 does not show the full annual ceiling. Before contributing, apply this shortcut: $72,000 minus employee deferrals minus employer contributions, then wait for the plan to confirm the result.
- Employee deferrals
- Employer contributions
- Catch-up amount
- Plan participation changes
Step 3: Ask who can keep the contribution
A voluntary after-tax contribution can be subject to the ACP nondiscrimination test, which may limit or refund contributions for highly paid employees. Ask the administrator how the test works, when refunds occur, and whether the plan credits earnings on returned money; ask the CPA how the refund and earnings would be reported.
A practice owner who sets payroll to the full calculated amount before confirming ACP treatment can receive a $5,000 refund after testing. That money comes back as cash, and the Roth contribution room for that year is gone. A payroll election does not lock the money in the plan. Keep liquidity available until the administrator explains how corrections and refunds are paid.
Step 4: Choose the conversion route and timing
Confirm whether the plan supports an immediate in-plan Roth conversion, a distribution to a Roth IRA, or both. The route affects paperwork, timing, account control, and tax reporting.
The IRS treatment separates contribution basis from earnings. After-tax contributions themselves are not taxed again when converted, but earnings converted with them are taxable. Delaying conversion without checking the plan can allow earnings to build and increase the taxable amount.
Assante Wealth Management asks for the administrator's conversion schedule before a payroll election is made. Knowing that conversions exist is the easy part. We want to know how many days the plan takes to convert each contribution and what confirmation the client gets afterward.
- In-plan Roth conversion
- Rollover to Roth IRA
- Conversion date
- Tax records
Step 5: Test the choice against the family cash calendar
A Roth contribution is not automatically a good use of cash. Kwame and Colleen need to reserve money for college bills beginning in two years, possible sale costs connected with Kwame's three-doctor primary-care practice, and the uncertainty around a possible $1.2 million sale.
Hypothetical: Kwame is 52 and Colleen is 50. Kwame's plan credits $15,000 of employer contributions during 2026, and he makes the full $24,500 employee deferral. The available room is $72,000 minus $24,500 minus $15,000, which equals $32,500.
He elects only $12,000 of after-tax contributions because $20,000 is reserved for college bills and sale costs. The plan converts the $12,000 promptly. Assume $100 of earnings accrue before conversion, so $12,000 is converted without tax on the contribution and $100 is taxable.
The formula works even though Kwame does not fill the room. His household has $1.3 million saved, but that money has jobs attached to it. A possible practice sale can change the timing of income, and tuition cannot be paid with a retirement account without creating another tax and access problem.
A different physician with ample taxable cash, stable employment, and a plan that confirms immediate conversions may fill more of the $32,500. Kwame and Colleen should contribute less if the election would force a $10,000 loan or a sale of investments for tuition. Investments can lose value, so a forced sale may return less than the amount invested.
The choice also affects Colleen and their adult children. Roth assets can be useful for estate planning, but beneficiary designations, inherited-account rules, and the family's cash needs still require review. A simple one-page plan should show the reserve, the contribution, and the conversion route.
| Task | Who does it | When | Output |
|---|---|---|---|
| Read plan terms | Kwame and administrator | Before payroll election | Feature confirmation |
| Calculate annual room | Kwame, CPA | Before contributions | $32,500 example room |
| Check ACP treatment | Administrator | Before and after year-end | Testing and refund rules |
| Convert after-tax money | Kwame and plan | Per plan schedule | Roth transaction record |
| Review tax forms | Kwame and CPA | After forms arrive | Tax reporting check |
- Possible practice sale
- $1.3 million saved
- College bills in two years
- Cash outside retirement accounts
Step 6: Which questions belong with the administrator and CPA?
The decision rule is short: calculate $72,000 minus employee deferrals and employer contributions, then contribute only after the plan confirms the feature, conversion route, testing treatment, and payroll timing. Ask who confirms the calculation, whether employer money is credited throughout the year, whether ACP testing can refund contributions, and how quickly conversions occur.
Put these questions in one message:
Ask the administrator:
Who confirms the $72,000 calculation?
When is employer money credited?
Can ACP testing refund contributions?
How quickly does conversion occur?
Ask the CPA:
What Form 1099-R entries may appear?
How are refunded earnings reported?
What changes after a practice sale?
Should Colleen's beneficiary designation change?
Assante Wealth Management would review the plan language, payroll schedule, employer contribution pattern, and tuition reserve before Kwame changes the election. Bring one question to that meeting: do this plan's Roth mechanics still work after the college and sale reserve is set aside?
- Plan administrator questions
- CPA questions
- Practice sale questions
- Beneficiary questions
Your questions about a mega backdoor Roth for doctors, answered
Does a 401(k) need both after-tax contributions and in-plan Roth conversions?
Yes, a 401(k) needs a workable contribution feature and a conversion or distribution route. After-tax contributions alone do not create Roth money automatically. The plan may permit an in-plan Roth conversion, a rollover of eligible amounts to a Roth IRA, or both. Confirm the route, timing, and tax reporting with the administrator and CPA.
Can a plan administrator change my after-tax election during the year?
A plan administrator may allow changes during the year, but the plan's payroll deadlines control. Some elections can be changed prospectively, while others require a waiting period or cannot be changed after payroll runs. Ask for the deadline in writing before changing your deferral or after-tax election.
What happens if after-tax money earns interest before conversion?
Earnings that accumulate before conversion are generally taxable when converted, while the after-tax contribution itself is not taxed again. A prompt conversion can reduce the earnings subject to tax, but the plan's records and transaction date control. Ask how the plan identifies contributions and earnings on the conversion paperwork.
Should I choose an after-tax 401(k) or keep the money in a taxable account?
An after-tax 401(k) contribution may offer a Roth conversion route, but a taxable account provides more accessible cash for tuition, practice costs, or a sale. Compare tax treatment, investment choices, conversion timing, testing risk, and liquidity. The better choice is not always the account with the largest annual contribution room.
Is this strategy available when my spouse is the business owner?
Yes, the strategy may be available when your spouse owns the business, but the business plan must permit voluntary after-tax contributions and a Roth conversion or eligible distribution. Employer contributions, plan testing, ownership rules, and the spouse's role can affect the calculation. Send the arrangement to both the administrator and the CPA so they review it at the same time.
How do I tell whether the plan applies the ACP test to my contributions?
Ask the plan administrator whether voluntary after-tax contributions are included in the actual contribution percentage, or ACP, test and how refunds are calculated. Also ask when testing occurs, how earnings are handled, and when corrections are paid. The plan's written explanation matters more than a payroll portal label.
Sources and further reading
This is general information, not advice tailored to your finances or circumstances. Investing involves risk, including the possible loss of principal. Before making any decision about money, taxes or your practice, talk with a professional who knows your full situation.