Mega Backdoor Roth
Category: Retirement & health
After-tax 401(k) contributions (beyond elective deferrals) that are converted or rolled to Roth, limited by the §415 annual additions cap and plan design.
How Mega Backdoor Roth fits 2026 planning
Mega Backdoor Roth sits inside retirement contribution limits, distribution timing, and how pre-tax vs Roth choices change AGI. For tax year 2026, US Tax Tools treats year-scoped constants (brackets, contribution limits, wage bases, credit schedules) as separate datasets — so explanations of Mega Backdoor Roth should be read with the same year selected in any linked calculator.
Category focus: Retirement & health. Readers usually land on this page while comparing a paycheck estimate, a credit phaseout, or a retirement contribution room figure that depends on understanding Mega Backdoor Roth first.
Worked example
If the §415 limit is $70,000 and employee plus employer amounts use $35,000, up to $35,000 of after-tax room may remain when the plan allows it.
Treat the example as a teaching sketch, not a filing position. Change filing status, state residency, or mid-year events and the same definition of Mega Backdoor Roth can produce a different cash outcome even when the glossary text stays the same.
What to watch for
Definitions of Mega Backdoor Roth can differ slightly across IRS publications, SSA rules, Marketplace subsidy worksheets, and state agencies. When two programs both say “income,” confirm which modification rules apply — MAGI for one credit is not always MAGI for another.
Legislation and inflation adjustments can move the dollar thresholds around Mega Backdoor Roth without renaming the concept. Prefer the effective date on the primary source (Rev. Proc., SSA notice, USDA table, or state DOR bulletin) over any blog summary — including this one if a later notice supersedes it.
Confirm how Mega Backdoor Roth appears on your forms by reading the IRS instructions for the schedules that match your facts. Educational definitions here cannot capture every exception or state overlay.
Next step
When you are ready to model numbers, open the Mega Backdoor Roth related calculator on US Tax Tools. Engines keep tax-year datasets separate so a 2025 habit does not silently reuse a 2026 constant.
Related reading: Tax insights for longer 2026 explainers, Methodology for how engines store cents and traces, and Disclaimer for educational-use limits.