Mega Backdoor Roth 401(k) in California
Unlock substantial Roth contributions if your plan supports after‑tax contributions and conversions. Built for FAANG & startup leaders in the Bay Area and Los Angeles.
Executive summary. The Mega Backdoor Roth (MBR) lets high earners move large sums into Roth each year via after‑tax (non‑Roth) contributions inside a 401(k), followed by an in‑plan Roth conversion or in‑service distribution to a Roth IRA. Not every plan supports it—two features are essential: (1) after‑tax contribution option and (2) a way to convert or distribute those after‑tax dollars regularly.
Want us to audit your plan for MBR eligibility?
We’ll verify features, model max contributions, set conversion cadence, and coordinate with your CPA for California tax nuances.
How the Mega Backdoor Roth works
- You make after‑tax (non‑Roth) contributions to your 401(k) beyond the standard pre‑tax/Roth deferral.
- Your plan converts those after‑tax dollars to Roth (in‑plan) or distributes them to a Roth IRA via in‑service rollover.
- Ideally, conversions occur as frequently as allowed (often automatic), limiting any taxable earnings in the after‑tax subaccount.
MBR is distinct from the regular “Backdoor Roth IRA,” which uses nondeductible IRA contributions + Roth conversion and is subject to the pro‑rata rule at the IRA level.
Plan feature checklist (must‑haves)
- After‑tax employee contributions allowed in the 401(k).
- In‑plan Roth conversion of the after‑tax subaccount or in‑service distribution of the after‑tax subaccount to a Roth IRA.
- Frequent conversion/rollover cadence (monthly/quarterly/automatic) to keep earnings minimal.
- Clear visibility of subaccount balances (pre‑tax, Roth, after‑tax) on statements.
If any of these are missing, the MBR may not be feasible or may create unexpected taxes.
Step‑by‑step setup
- Confirm eligibility: Ask HR/benefits for the Summary Plan Description (SPD) and adoption agreement pages that show after‑tax and in‑plan Roth or in‑service distribution features.
- Set after‑tax percentage: Choose a rate that, along with employer contributions and your standard deferrals, fills (but does not exceed) the annual additions limit under IRC §415(c).
- Turn on automatic conversions (if available) or schedule periodic in‑service rollovers to a Roth IRA.
- Monitor payroll & employer true‑ups to avoid overshooting limits; adjust mid‑year as needed.
- Coordinate with taxes: Track basis vs. earnings; earnings converted/rolled are taxable.
Contribution math & examples
The ceiling
The maximum you can get into the plan each year is the IRS annual additions limit (IRC §415(c)). Your available room for after‑tax contributions equals:
After‑Tax Room = 415(c) limit − (your pre‑tax/Roth deferrals + employer match/profit share)
Limits change annually. Always verify the current year’s 415(c) and elective deferral limits on IRS.gov before setting rates.
Example — FAANG Director (Bay Area)
- Max pre‑tax/Roth deferral via payroll
- Employer match + profit share credited
- Set after‑tax to fill remaining 415(c) room
- Automatic in‑plan conversion each pay period
Result: Large annual Roth additions without waiting for IRA limits.
Example — Startup VP (Los Angeles)
- Plan allows in‑service distributions to Roth IRA
- Quarterly sweep of after‑tax subaccount
- Minimal earnings → small taxable amount at rollover
Result: Builds Roth IRA rapidly while staying within plan rules.
Common pitfalls to avoid
- Plan doesn’t truly support MBR. After‑tax without conversion/rollover access is a red flag.
- Overcontributing past 415(c). Employer true‑ups can push you over—watch the totals.
- Letting earnings build up. Infrequent conversions can create unnecessary taxable income.
- ACP testing issues. High after‑tax contributions can trigger refunds in some plans; confirm testing treatment.
- Mislabeling contributions. Ensure you’re selecting after‑tax (non‑Roth)—not Roth elective deferrals.
We’ll model max contributions—and keep you compliant.
We coordinate payroll, employer contributions, conversion cadence, and tax reporting so you don’t blow past limits.
FAQ
Is the Mega Backdoor Roth affected by income limits?
No income limit applies inside the 401(k). Eligibility depends on plan features, not your MAGI.
Can I do both a Backdoor Roth IRA and Mega Backdoor Roth?
Yes, if you’re eligible for both. The IRA pro‑rata rule applies at the IRA level; the MBR occurs inside the 401(k).
Does California tax the conversion?
Conversions of after‑tax basis are not taxed; any earnings converted are taxable at both federal and California levels in the year converted.
Will my plan’s nondiscrimination testing limit me?
Some plans restrict or refund after‑tax contributions due to ACP testing. Confirm how your plan treats after‑tax and whether automatic conversion helps.
References & further reading
- IRS — 401(k) contribution limits (elective deferrals)
- IRS — IRC §415(c) annual additions limit
- IRS — In‑plan Roth rollovers
- Plan docs — Summary Plan Description (SPD) & adoption agreement (ask HR/benefits)
This material is for informational purposes only and not tax, legal, or investment advice. Contribution limits and plan rules change—verify on IRS.gov and with your plan administrator. RYSE Financial is a fee‑based advisory firm.