Decode your plan.
Size your Mega Backdoor Roth room.
A three-question SPD decoder tells you whether your 401(k) supports it. A deterministic §415(c) calculator sizes your remaining after-tax room for the year. No tabloid framing, no urgency triggers — statute-cited verdicts, nothing logged.
- 3
- Decoder questions
- $72,000
- §415(c) limit 2026
- $0
- Inputs logged
01 · The tools
Two questions, answered with your numbers
Eligibility first, then capacity. Both run in your browser — the personalized output is what an AI Overview cannot compress.
Does your plan permit the Mega Backdoor Roth?
Three questions about your Summary Plan Description. The same three answers always produce the same verdict — deterministic and statute-cited. Nothing is logged.
Awaiting inputs — answer Q1 to compute the verdict
How much Mega Backdoor Roth room remains?
Deterministic §415(c) math with your numbers substituted in. Reproducible by hand and verifiable against the worked examples. Nothing is logged.
Live formula — §415(c) overall limit (2026)
room = §415(c)2026 − deferral − employer − after_tax
= $72,000 − $24,500 − $20,000 − $0
= $27,500
$27,500
$2,115 per pay period over 13 remaining periods
Already counted toward §415(c): $44,500 of $72,000
§415(c) capacity
The §402(g) age-50+ catch-up does not count against §415(c) — it sits on top of the annual-additions limit, so it is not subtracted here. Independent CPA / CFP review in progress
One hub, not four tabs
Today you read a CPA blog, cross-check an employer list, decode your SPD by hand, and run a separate calculator. This consolidates all four.
02 · Employer plan registry
Plan archetypes, graded by source
Illustrative archetypes of common tech-employer 401(k) configurations — support flag, conversion mechanic, contribution mechanic, and confidence tier. Verify your own plan with HR; these teach the patterns, they are not claims about a specific company.
Large cloud platform
Cloud / infrastructure
- mechanic
- In-plan Roth conversion
- contrib
- Per pay period
- source
- Illustrative archetype
Social platform
Consumer internet
- mechanic
- In-plan Roth conversion
- contrib
- Per pay period
- source
- Illustrative archetype
Marketplace retailer
E-commerce
- mechanic
- No conversion path
- contrib
- Not applicable
- source
- Illustrative archetype
Productivity software co.
Enterprise software
- mechanic
- In-plan Roth conversion
- contrib
- Per pay period
- source
- Illustrative archetype
Device hardware maker
Consumer hardware
- mechanic
- In-service distribution
- contrib
- Per pay period
- source
- Illustrative archetype
Payments infrastructure
Fintech
- mechanic
- In-plan Roth conversion
- contrib
- Per pay period
- source
- Illustrative archetype
Streaming media co.
Media / streaming
- mechanic
- No conversion path
- contrib
- Not applicable
- source
- Illustrative archetype
Accelerated computing co.
Semiconductors
- mechanic
- In-plan Roth conversion
- contrib
- Per pay period
- source
- Illustrative archetype
Enterprise CRM platform
Enterprise software
- mechanic
- In-service distribution
- contrib
- Annual / lump-sum
- source
- Illustrative archetype
Ride-hailing platform
Mobility
- mechanic
- In-plan Roth conversion
- contrib
- Per pay period
- source
- Illustrative archetype
03 · Learn
Pillar guides
Long-form, statute-cited, reviewer-attributed. Each pillar surfaces the live tools above the fold — interactive output is the AI-Overview defense.
/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.
04 · Trust & methodology
How we research
Source-of-truth hierarchy
Employer plan flags grade against a four-tier hierarchy: official benefits page, then Form 5500 filing, then Levels.fyi, then Carry. Each card surfaces its tier and confidence.
No fabricated limits
Every IRS dollar figure is transcribed from the official COLA notice with a primary-source link and a last-verified date. Published figures are never edited in place.
Deterministic math
The decoder verdict and the capacity number are pure functions of your inputs — reproducible by hand, unit-tested against IRS-anchored worked examples.
Reviewer attribution
No credentialed reviewer is engaged yet. Until a CPA / CFP / EA signs on and is named here, the site says so plainly rather than inventing a name — treat every page as educational.
05 · FAQ
Common questions
Two minutes to a statute-cited answer
Decode your plan, then size your room. Free, deterministic, and nothing you enter leaves your browser.