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Mega Backdoor Roth, explained without the fluff
/learn/what-is-mbr
What is the Mega Backdoor Roth?
The after-tax 401(k) bucket plus an in-plan conversion or in-service distribution. Limit tables for 2025 and 2026.
/learn/spd-decoder-explained
The 3 SPD sentences that decide eligibility
What to look for in your Summary Plan Description, with publicly-citable language patterns for each verdict.
/learn/in-plan-vs-in-service
In-plan conversion vs in-service distribution
The two conversion mechanics, their tax treatment, basis tracking, and how the Form 8606 reconciliation differs.
/learn/form-8606-walkthrough
Form 8606 walkthrough
Line-by-line, Mega-Backdoor-Roth-specific basis tracking for the in-service-distribution path.
/learn/form-1099r-5498
1099-R and 5498 reconciliation
Why the conversion produces both forms, and how to read them so the numbers do not double-count.
/learn/capacity-calc-formula
The §415(c) capacity formula
Overall limit minus elective deferral minus employer additions equals remaining after-tax room — with worked examples.
/learn/per-pay-vs-annual
Per-pay-period vs annual contribution
Plans that require per-pay after-tax contributions: missing a paycheck can forfeit that period's room for the year.
/learn/legislative-tail-risk
Legislative tail risk
The Build-Back-Better-era proposed closure: not active law, not zero risk over a multi-year horizon. Informational only.