The L3 Ch2 L1 screen advanced 18-22 households to the per-client sizing memo workflow. The screen produced a preliminary recommended-conversion-size for each, but the deep math was deferred to this lesson. The L3 Ch2 L2 per-client sizing memo runs the household-level computation: federal bracket fill to top of 22% or 24%, NIIT 3.8% at the right thresholds, IRMAA two-year lookback (2024 AGI for 2026 conversion year — avoiding the next-tier cliff), state tax at the client domicile, the pro-rata rule check against aggregated pre-tax IRA basis under IRC §408(d)(2) read with §72(e)(8) Form 8606 lines 6-15 (not §408(d)(6) which governs IRA transfers incident to divorce), and the separate-conversion five-year clock implications per §408A(d)(3). The output is a propose-mode memo the senior advisor reviews, modifies with documented judgment, and converts to a Reg BI recommendation by signing at L3 Ch2 L3.

From Screen Output to Deep Math

The screen output's recommended-conversion-size column held a preliminary number derived from a relatively coarse leverage calculation. The sizing memo runs the precise math per household using the structured-output JSON object from the screen as input, the full Holistiplan extraction, the full RightCapital plan, the aggregated custodian-feed positions and basis, and the household-state context from Wealthbox. The sizing memo's deliverable is a propose-mode memo with the exact conversion size, the rationale linked to each component, the alternatives considered, the projected post-conversion AGI, the projected IRMAA tier impact in year+2, the pro-rata-rule impact in dollars, and the multi-year-ladder framing if applicable.

The memo's central computational engine is the multi-component cost decomposition. For a proposed conversion amount X, the total current-year cost = federal-marginal-tax(X) + NIIT(X if applicable) + state-tax(X at domicile rate) + IRMAA-cliff-incremental(X if next-tier crossed) + pro-rata-induced-extra-tax-from-aggregated-basis-mechanics. Each component is computed separately, the sum is the total cost, and the leverage ratio is total-current-cost divided into the household's projected lifetime tax savings. The senior advisor's judgment may adjust the proposed X downward to leave margin from a cliff, upward to capture additional bracket-fill value, or sideways to coordinate with concurrent planning workflows.

Bracket Fill to Top of 22% or 24% — The Federal-Marginal Component

The federal-marginal component is the dominant cost driver for most conversions. The 2026 federal brackets (MFJ; single-filer thresholds are half) place the 22% bracket from approximately $96,950 to $206,700 taxable income, the 24% from $206,700 to $394,600, the 32% from $394,600 to $501,050, and the 35% from $501,050 to $751,600 — with the 12% bracket below and the 37% top bracket above. The sizing memo's bracket-fill decision is between three target ceilings: top of 22%, top of 24%, top of 32% (rarely worth pursuing).

For most pre-RMD-window or pre-SS-window clients with modest current AGI, bracket fill to top of 24% is the conversion sweet spot — the 24% bracket is materially below the post-RMD-era 32% / 35% bracket compression most large-IRA-holder households project into. The math: a household with current AGI $148,000 and MFJ status has roughly $30,000 of standard deduction yielding $118,000 taxable, sitting in the 22% bracket. The bracket-fill to top of 24% is approximately $276,600 taxable, requiring ~$159K of additional income (conversion) added to AGI. The bracket-fill to top of 22% is approximately $88,700 taxable additional (~$118K conversion). The differential — converting another $41K to push from top-of-22% to top-of-24% — costs marginal 24% federal vs avoided future 32% or 35% — net positive leverage on the differential.

The sizing memo's bracket-fill math is layered onto the Holistiplan-extracted prior-year baseline and RightCapital's current-year projection of pre-conversion AGI. Any current-year income changes (job change, bonus, RSU vesting captured from L2 Ch2 L1 prospect research or annual review transcript) update the baseline. The proposed conversion size is the gap from projected pre-conversion AGI to the target bracket-fill ceiling, expressed in dollars added to AGI.

NIIT and State-Tax Components

NIIT (Net Investment Income Tax) at 3.8% applies to investment income (capital gains, dividends, interest, rental income, passive income) above $200K (single) or $250K (MFJ) modified AGI thresholds. The conversion itself is ordinary income, not investment income, so the conversion amount is not directly subject to NIIT. But the conversion raises MAGI, which can pull investment income that was previously below the threshold above it, triggering NIIT on the investment income portion. The sizing memo computes the NIIT-cliff impact: if pre-conversion MAGI plus investment income is below the threshold, and post-conversion MAGI plus investment income crosses, the incremental NIIT is 3.8% × (investment income above threshold post-conversion).

State tax at the client domicile is straightforward arithmetic. The marginal state rate × conversion amount = state-tax cost. California (top 13.3%), New York (top 10.9%), New Jersey (top 10.75%), Hawaii (top 11%) are the high-tax-state outliers; Texas, Florida, Tennessee, Nevada, Wyoming, South Dakota, Washington (no state income tax on retirement income for most retirees) are the zero-state-tax outliers. A client domiciled in California paying top marginal rate on a $74K conversion incurs ~$9.8K state-tax cost — material to the leverage. A client planning to move to Florida pre-RMD has a different long-term-savings calculation that the memo's lifetime-savings component must capture.

IRMAA Two-Year Lookback — Avoiding the Next-Tier Cliff

The IRMAA Income-Related Monthly Adjustment Amount is the Medicare premium surcharge tied to AGI two years prior. The 2026 IRMAA tier determination uses 2024 AGI. The Q4 2026 conversion year's IRMAA impact lands in 2028 Part B and Part D premiums. The CMS-published 2026 thresholds (illustrative — verify against current CMS) at MFJ approximately: Tier 0 (base premium) AGI ≤ $206,000; Tier 1 $206,001-$258,000; Tier 2 $258,001-$322,000; Tier 3 $322,001-$386,000; Tier 4 $386,001-$750,000; Tier 5 above $750,000. Each tier-crossing adds ~$70-$80/month for Part B and additional for Part D × 2 people for joint Medicare household × 12 months = roughly $1,800-$3,600 additional annual cost per tier crossed, per couple.

The cliff math: a household at projected post-conversion AGI of $322,500 sits 500 dollars over the Tier 2 cap and pays full Tier 3 premium for the entire year — the cliff is sharp, not graduated. The sizing memo flags any proposed conversion that would push the household across a tier and recommends sizing back to leave a margin (typically $5-10K below the cap to absorb any income-projection error). The Hendersons example sized at $74K rather than $96K specifically to preserve Tier 2 IRMAA position.

The memo's IRMAA computation: pre-conversion projected 2026 AGI + proposed conversion amount = post-conversion projected AGI; compare to 2026 CMS tier table; identify tier crossing if any; compute incremental IRMAA premium cost in 2028 (both spouses if joint); discount to present value if comparing across years; flag in the leverage calculation as a current-year cost-equivalent (technically a year+2 cost but treated as cost of the conversion year decision).

The Pro-Rata Rule Deep Dive — IRC §408(d)(2) + §72(e)(8) Form 8606

The pro-rata rule under IRC §408(d)(2) (the IRA aggregation rule) read with §72(e)(8) (basis recovery formula) — reported on Form 8606 lines 6 through 15 — controls the taxable portion of any IRA distribution or conversion when the IRA owner has after-tax basis in any traditional/SEP/SIMPLE IRA. The rule aggregates ALL of the IRA owner's traditional/SEP/SIMPLE IRA balances at year-end (Form 8606 line 6) plus all conversions and distributions during the year (Form 8606 line 7) = the aggregated denominator. The numerator is the total basis (line 5: basis as of beginning of year + line 1: new nondeductible contributions for the year). The taxable portion of any conversion is (1 - basis/aggregated total) × conversion amount.

The sizing memo's pro-rata computation: pull aggregated pre-tax basis from all custodian feeds and prior Form 8606 historical filings (the basis carryforward from prior nondeductible contributions, prior conversions, etc.); pull current-year-end aggregated IRA balances; compute the basis-to-total ratio; apply to the proposed conversion amount; the taxable-portion is added to AGI for the federal-marginal / NIIT / state / IRMAA computations; the non-taxable basis-recovery portion is tax-free Roth conversion.

The §408(d)(6) distinction is critical: §408(d)(6) governs IRA transfers incident to divorce (the receiving spouse takes the IRA as their own with basis-tracking implications) and is a completely separate provision from §408(d)(2). The program-wide audit explicitly flagged §408(d)(6) miscitation in earlier drafts; the sizing memo's regulatory checkpoint catches any AI output that confuses the two. Form 8606 is the operational artifact for both basis tracking (lines 6-15) and basis-carryforward (line 14).

Pro-Rata Mitigation Strategies

When aggregated pre-tax IRA basis is non-zero, the pro-rata impact reduces the conversion's net benefit. The sizing memo's options analysis: (a) accept the pro-rata cost as part of total cost (often appropriate if basis ratio is low); (b) roll the aggregated pre-tax IRA balance into a 401(k) plan if the plan-document accepts rollovers-in, leaving only after-tax basis in the IRA — this is the prerequisite for a clean backdoor Roth (L3 Ch3 L3); (c) defer conversion to a future year when basis ratio is more favorable (rare); (d) coordinate with QCD strategy under §408(d)(8) which can reduce aggregated balance (and Form 8606 line 6) over time for the 70.5+ household; (e) coordinate with charitable bunching using appreciated stock for the basis-equivalent year.

Five-Year Clock Implications — IRC §408A(d)(3)

Roth IRAs carry two distinct five-year clocks. The contribution clock (IRC §408A(d)(2)(B)) starts with the first contribution to any Roth IRA and runs continuously; tax-free withdrawal of earnings requires the five-year period plus a qualifying event (age 59½, death, disability, first-time home purchase up to $10K). The conversion clock (§408A(d)(3)(F)) is separate per conversion year: each year's converted amount has its own five-year clock for tax-free penalty-free withdrawal of the converted principal (the basis from prior years' conversions retains its own clock).

The sizing memo's clock implications: the client must be aware that the converted amount is not available for tax-free penalty-free withdrawal of the converted principal for five years from the conversion year (until the client reaches 59½, where the conversion clock becomes moot but the contribution clock for earnings still applies); a client under 59½ converting at $74K creates a 5-year-lock on those funds; a 2026 conversion runs through 2030; the multi-year ladder strategy creates a layered set of clocks that the memo documents per year.

The conflation of contribution clock with conversion clock is a known AI-hallucination failure mode (cited in L1 Ch2). The regulatory checkpoint catches any output that confuses the two.

The Multi-Year Ladder Framing

The single-year sizing analysis often points toward a multi-year ladder strategy: instead of one $200K conversion in 2026, do four $50K conversions over 2026-2029. The ladder spreads the current-year cost across multiple years, maintains bracket fill at the optimal target each year, manages IRMAA tier exposure across multiple two-year-lookback windows, and creates a layered set of five-year clocks for staged tax-free penalty-free access to converted principal.

The sizing memo evaluates ladder vs single-year via lifetime leverage comparison: single-year aggressive conversion produces front-loaded current cost but earlier tax-free growth; multi-year ladder produces smoother cost distribution but later cumulative tax-free growth. The math typically favors ladder when the client has a long pre-RMD horizon (multi-year ladder benefits from cost smoothing) and single-year-aggressive when the client has a specific window (post-business-sale low-income year that won't recur).

The memo's ladder output is a year-by-year table per L2 Ch8 L2 Markdown-table format showing year, pre-conversion AGI projection, recommended conversion, post-conversion AGI, federal bracket position, IRMAA tier position, conversion tax, lifetime LT benefit (similar to the L2 reference table in the structured-output lesson). The senior advisor reviews the ladder and may approve, modify, or substitute a single-year alternative.

The Hendersons' Sized Memo — Worked Example

The Hendersons (married couple 64 and 62, $2.4M total, $148K AGI 2025 baseline) advance to L3 Ch2 L2 from the screen. The sizing memo runs the deep math.

Pre-conversion baseline: Holistiplan-extracted 2025 AGI $148,000; 2026 projected AGI (no conversion) $151,000 (modest growth in dividend income and Social Security delayed); MFJ standard deduction $30,000 (2026); projected taxable income $121,000; 22% bracket position.

Bracket-fill analysis: Top of 22% bracket 2026 ~$206,700 taxable, ~$236,700 AGI for MFJ standard deduction → fill gap $85,700 to top of 22%. Top of 24% bracket ~$394,600 taxable, ~$424,600 AGI → fill gap $273,600 to top of 24%.

IRMAA analysis: Pre-conversion 2026 AGI $151,000 below Tier 0 cap. Top-of-22% conversion (~$85,700) post-AGI $236,700 — Tier 1 territory; incremental ~$1,800/yr each in 2028 Part B/D × 2 = ~$3,600/yr extra Medicare. Top-of-24% conversion (~$273,600) post-AGI $424,600 — Tier 4 territory; incremental cost steeper. The cliff between Tier 2 ($258,001-$322,000) and Tier 3 ($322,001-$386,000) is the operative constraint — converting up to $171,000 keeps Tier 2; converting $172,001 crosses to Tier 3 and pays full Tier 3 premium for the year.

Pro-rata check: Hendersons' aggregated traditional/SEP/SIMPLE IRA balance $1,400,000 across Schwab + Fidelity; aggregated basis $0 (all pre-tax contributions over career); pro-rata ratio basis/total = 0%; conversion is 100% taxable (no basis recovery). Clean from pro-rata perspective. (Note: §408(d)(2)+§72(e)(8) Form 8606 — not §408(d)(6) divorce.)

State tax: Hendersons domiciled in Texas (no state income tax on retirement income). State-tax cost $0.

NIIT check: Hendersons' investment income $32,000 (dividends + interest). Pre-conversion MAGI + investment income $151K + $32K = $183K. Below $250K MFJ threshold. Conversion of $74K pushes MAGI to $225K, MAGI+inv $257K, crossing threshold; NIIT applies to the $7K excess at 3.8% = $266. Modest.

Five-year clock: Both Hendersons 59½+; conversion clock implications moot for penalty-free withdrawal of converted principal; tax-free withdrawal of earnings still requires contribution-clock five-year period from first Roth contribution (already met).

Proposed conversion size: $74,000 — fills part of the 22%-to-24% bracket transition, stays well within Tier 2 IRMAA, manages NIIT exposure to $266, $0 state tax, 100% taxable (no pro-rata), 5-year clock moot (both over 59½). Total current-year cost: federal-marginal-tax(74K) ≈ $17,300 + NIIT $266 + state $0 + IRMAA-incremental Tier 2 vs Tier 0 ≈ $3,600 in 2028 = ~$21,166 total. Lifetime savings: projected reduced RMDs at age 73-95+, surviving-spouse single-filer bracket compression after first death, reduced lifetime IRMAA = ~$51,000 lifetime present value. Leverage ratio: 51,000 / 21,166 = 2.41 — matches the screen's preliminary 2.4 leverage estimate.

Coordination flags: Higher-earner SS delay to 70 (separate L3 Ch4 L1 memo); trust funding line item open since 2022 (L2 Ch5 L2 IPS update with attorney handoff); November tax-planning check-in scheduled with CPA.

Alternatives considered: (a) No conversion — leaves Hendersons exposed to RMD-driven bracket compression at 73; rejected. (b) $24K conversion — under-uses the bracket fill, leverage lower; rejected. (c) $74K conversion — recommended. (d) $96K bracket-fill maximum — pushes closer to Tier 2 ceiling, less margin, marginally higher leverage but ~30% higher current-year cost; rejected for margin preservation. (e) Multi-year ladder $40K × 4 years — modest improvement in cost smoothing but no near-term cliff and SS delay creates 2-3 year window where the ladder is appropriate; documented for next-year re-evaluation.

The Propose-Mode Output

The sizing memo's output is a propose-mode JSON object per the regbi-conversion-memo-schema v2.1: household_id, memo_date, recommended_conversion_amount, bracket_fill_analysis, NIIT_check, IRMAA_two_year_lookback_projection, state_tax_impact, pro_rata_check_against_aggregated_pre_tax_basis (citing §408(d)(2)+§72(e)(8) Form 8606 — not §408(d)(6)), five_year_clock_implications, alternatives_considered_summary, coordination_dependencies, leverage_ratio_summary, total_current_year_cost, projected_lifetime_savings, senior_advisor_review_required_flag. The output is structured for L3 Ch2 L3 ingestion into the Reg BI-compliant recommendation memo workflow.

The senior advisor reviews the propose-mode output, applies judgment per the L3 Ch1 L2 handoff diagram, modifies as needed, and authorizes advancement to L3 Ch2 L3. The three-tier verification per L3 Ch1 L3 produces source-system + regulatory + client-fit checkpoint logs that route to the Smarsh archive with tagged-Markdown metadata. The senior-advisor judgment narrative captures the documented application of judgment that becomes the Reg BI Care Obligation evidence at L3 Ch2 L3.

Key Takeaways

• The sizing memo runs the deep math the screen deferred. Federal-marginal + NIIT + state + IRMAA cliff + pro-rata impact computed per household with full Holistiplan / RightCapital / custodian / Wealthbox context.
• Bracket fill to top of 22% or 24% is the federal-marginal component decision. Most pre-RMD / pre-SS clients target top of 24% as the conversion sweet spot, materially below the post-RMD 32%/35% bracket compression most large-IRA households project.
• NIIT 3.8% applies when conversion-induced AGI lift pushes investment income above $200K single / $250K MFJ thresholds. Conversion itself is ordinary income, not investment income, but MAGI rise triggers NIIT on the investment income portion that crosses the threshold.
• IRMAA cliffs are sharp. Crossing the next-tier cap by $1 pays full higher-tier premium for the year. The sizing memo flags any proposed conversion that crosses a tier and recommends sizing back to leave $5-10K margin from the cap.
• Pro-rata rule under IRC §408(d)(2) read with §72(e)(8) — Form 8606 lines 6-15 — controls the taxable portion when aggregated pre-tax basis is non-zero. (Not §408(d)(6) which governs IRA transfers incident to divorce.) Mitigation: roll pre-tax to 401(k) plan if plan-document permits, defer conversion, or accept pro-rata cost.
• Five-year clocks under IRC §408A(d)(3) — separate per conversion year — locks the converted principal for tax-free penalty-free withdrawal until five years pass (or age 59½ if earlier). Conflation with the contribution clock is a known AI failure mode.
• Multi-year ladder vs single-year aggressive is the lifetime-leverage comparison. Ladder favored for long pre-RMD horizons (cost smoothing); single-year favored for specific windows that won't recur (post-business-sale, sabbatical year).
• The Hendersons sized memo: $74K conversion, leverage 2.41, total current cost ~$21K (federal $17.3K + NIIT $266 + state $0 + IRMAA-incremental $3.6K), lifetime savings ~$51K PV, four alternatives considered, coordination flags for SS-delay and trust-funding, propose-mode output for L3 Ch2 L3 advancement.