Mega Backdoor Roth (2026)

Mega backdoor Roth mechanics

When a 401(k) plan allows after-tax employee contributions plus either in-plan Roth conversion or in-service rollover to Roth IRA, high earners can exceed the $24,500 elective deferral limit by stuffing after-tax dollars up to the Section 415(c) annual additions limit, then converting to Roth with minimal tax if basis is tracked correctly.

Room ≈ min(compensation, §415 limit) − employee deferrals − employer contributions. You enter compensation, deferrals, employer match/profit sharing, and the §415 dollar limit for your year (inflation-adjusted).

2026 deferral limits

For 2026, the IRA contribution limit is $7,500 with a $1,100 catch-up at age 50 and older. Elective deferrals to 401(k), 403(b), and most workplace plans cap at $24,500, with catch-up contributions of $8,000 at age 50+ and an enhanced $11,250 catch-up for ages 60 through 63 under SECURE 2.0. HSA limits are $4,400 for self-only HDHP coverage and $8,750 for family coverage, plus a $1,000 catch-up at 55+. Social Security wages for payroll tax purposes stop at the $184,500 wage base (SSA 2026).

Plans must explicitly allow after-tax contributions and conversions—many do not. Excess deferrals or failed ADP/ACP tests create corrective distributions.

Tax on conversion

Convert soon after after-tax contribution to minimize earnings taxed as ordinary income. Track Form 8605 basis in Roth IRA if rolling out of plan.

Related tools

401(k) calculator, Roth conversion calculator, contribution limits maximizer.

Sources

IRC §§402(g), 415(c); Rev. Proc. 2025-32 deferral limits.

Documentation and recordkeeping

Keep copies of forms, notices, and account statements that support numbers you enter. IRS audits and state reviews often start with mismatches between third-party reporting and what you claimed. Reconcile calculator outputs to official worksheets before filing.

When to revisit your estimate

Life changes mid-year—marriage, divorce, a move, bonus income, or a new job—can shift brackets, credits, and phaseouts. Rerun the tool when those events occur rather than relying on a January estimate through December.

State and local taxes

This page focuses on federal rules unless noted. Many states piggyback on federal AGI or MAGI definitions but apply their own rates and credits. Pair federal estimates with the state income tax calculator when residency matters.

Professional guidance

Complex returns—AMT, NIIT, multi-state income, business ownership, or large conversions—benefit from a CPA or enrolled agent who can sign the return. Calculators here show the math chain; they do not replace personalized advice or e-file validation.

Methodology on this site

Core 2026 federal brackets, deductions, and payroll limits follow IRS Rev. Proc. 2025-32, SSA wage-base announcements, and CMS Medicare premium tables where applicable. We show assumptions in the result panel when a rule is simplified for education.

Quarterly check-ins

Retirees and self-employed filers should revisit estimates after each quarter when investment income, required distributions, or business profit shifts. Waiting until December limits your options for withholding adjustments and timely estimated payments.

Documentation and recordkeeping

Keep copies of forms, notices, and account statements that support numbers you enter. IRS audits and state reviews often start with mismatches between third-party reporting and what you claimed. Reconcile calculator outputs to official worksheets before filing.

When to revisit your estimate

Life changes mid-year—marriage, divorce, a move, bonus income, or a new job—can shift brackets, credits, and phaseouts. Rerun the tool when those events occur rather than relying on a January estimate through December.

State and local taxes

This page focuses on federal rules unless noted. Many states piggyback on federal AGI or MAGI definitions but apply their own rates and credits. Pair federal estimates with the state income tax calculator when residency matters.

Professional guidance

Complex returns—AMT, NIIT, multi-state income, business ownership, or large conversions—benefit from a CPA or enrolled agent who can sign the return. Calculators here show the math chain; they do not replace personalized advice or e-file validation.

Methodology on this site

Core 2026 federal brackets, deductions, and payroll limits follow IRS Rev. Proc. 2025-32, SSA wage-base announcements, and CMS Medicare premium tables where applicable. We show assumptions in the result panel when a rule is simplified for education.

Quarterly check-ins

Retirees and self-employed filers should revisit estimates after each quarter when investment income, required distributions, or business profit shifts. Waiting until December limits your options for withholding adjustments and timely estimated payments.

Reading official publications

IRS Publications and Instructions often walk through worksheets line by line. When our simplified path differs from a form worksheet, trust the form for filing and use this page for directional planning only.

Calculator directory

Browse related tools from the calculator directory when your question spans credits, payroll, retirement, and investment tax in the same year.

Withholding versus liability

Paycheck withholding and estimated tax payments are cash-flow tools. They are not the same as annual tax liability computed on the return. Use the W-4 withholding calculator and quarterly estimated tax calculator when you need payment timing, not just liability.

Standard deduction reminder

The 2026 standard deduction is $16,100 for single and married filing separately filers, $24,150 for head of household, and $32,200 for married filing jointly (IRS Rev. Proc. 2025-32). Itemized filers must beat those amounts on Schedule A for itemizing to win.

Documentation and recordkeeping

Keep copies of forms, notices, and account statements that support numbers you enter. IRS audits and state reviews often start with mismatches between third-party reporting and what you claimed. Reconcile calculator outputs to official worksheets before filing.

When to revisit your estimate

Life changes mid-year—marriage, divorce, a move, bonus income, or a new job—can shift brackets, credits, and phaseouts. Rerun the tool when those events occur rather than relying on a January estimate through December.