First-time buyer navigating down payment assistance, FHA/conventional loan choice, PMI, closing costs, and affordability stretch in a high-rate environment.
MB-01 is the underwriting-edge archetype: borrowers with debt-to-income ratios pressed against the QM/ATR ceiling, layered down-payment-assistance stacks, and FHA-versus-conventional decisions that swing on a few basis points of PMI.
MB-01 exists because origination, disclosure, and affordability flows fail in characteristic ways at the threshold where a borrower first becomes one. These households test the surfaces governed by TRID timing (LE within three business days, CD three business days before consummation), RESPA Section 8 anti-kickback constraints when DPA programs route through preferred lenders, and the QM/ATR rule's 43% back-end DTI threshold — which most of this corpus pushes against. FHA, conventional 97, HomeReady, and a half-dozen state and municipal DPA programs each carry their own PMI/MIP arithmetic, seller-concession caps, and gift-letter sourcing requirements, and the right answer to 'which loan product' depends on a fee comparison that a lot of consumer-facing tools get wrong.
The structural story is a thin balance sheet pushed hard. Median income sits around $66k, median liquid net worth is roughly $43k, and 10 of 15 corpus households have already closed — meaning the down payment, closing costs, and any DPA second lien have already cleared the balance sheet, often leaving the emergency-fund goal underfunded. Three goals dominate behind retirement: debt payoff, emergency fund, and (for the renters) home purchase itself. Credit-card balances appear in every household; the typical posture is a borrower whose revolving utilization moves the rate sheet.
What distinguishes MB-01 from adjacent accumulation-early profiles is the bias of every dollar toward the housing transaction. Unlike F-03 (DINK savers building toward a future purchase) or A-01 (young family with the home already comfortably owned), MB-01 households are mid-transaction or freshly post-close, with HMDA-reportable application data still warm in the file. Single-parent and single-earner households are well represented, which materially affects DTI calculation and the FHA non-occupant-co-borrower question in ways the corpus surfaces explicitly.
Aggregated across the 15 MB-01 households in the shipped v3 corpus corpus. Numbers describe the corpus, not population claims.
Madison is a single-parent buyer in Nebraska whose $231k of total liabilities against only $6.3k of liquid reserves shows what a post-close MB-01 balance sheet actually looks like: a freshly originated mortgage stacked on existing revolving debt, with the emergency-fund cushion absorbed by closing. Her debt-payoff goal is on track because the budget was sized for it; the home-purchase and education-funding goals are flagged off-track in the same household because the dollar that would fund them is already booked to P&I. This is the file that breaks affordability calculators that compute DTI on a borrower's prior balance sheet rather than the post-close one.
Every MB-01 household ships with — at minimum — these JSON fields populated. The full schema is documented in the data set you purchase.
Mortgage-origination platforms use MB-01 to regression-test LOS workflows where a borrower's AUS findings flip between Approve/Eligible and Refer with Caution as DPA second liens, gift funds, and seller concessions are added or removed. Compliance and fair-lending teams use it to populate HMDA LAR records with the full spectrum of action-taken codes and to test ECOA adverse-action notice templates for borrowers near the cliff. Consumer-facing affordability tools and broker rate-shopping engines use it to stress-test the FHA-versus-conventional product comparison, including the MIP-cancellability tradeoff and the conventional 97 income-limit cutoff for HomeReady.
MB-01 explicitly excludes jumbo, second-home, and investment-property originations — those underwriting flows belong to MB-03 (DSCR / portfolio lender) for non-owner-occupied and to H-01 / H-02 for high-balance primary residences. Distressed servicing scenarios — modification, forbearance, short sale — are MB-02 territory by design; an MB-01 file that goes 60+ days delinquent should migrate to MB-02 for the workout flow. Households where the down payment is sourced from a recent inheritance live in E-01, not MB-01, because the gift-versus-inheritance documentation and tax basis tracking diverge. Borrowers stretching DTI on student-loan IDR payments specifically — where the IDR payment amount is the determinative DTI input — overlap with SL-01 and SL-02; if the loan product hinges on IDR-payment-as-DTI-input treatment, reach for those.
Income and credit-balance bands during v3 synthesis were informed by HMDA public LAR data, CFPB consumer credit panel summaries, and NAR first-time-buyer share reports for the relevant origination years. State concentration (IL, IA, CA) reflects a sampling choice rather than a HMDA share match, and the corpus is not stratified to mirror any specific year's first-time-buyer cohort. Per CLAUDE.md §9 the v3 households are FROZEN and not regenerable from current code; calibration claims here are descriptive of the priors that shaped synthesis, not auditable distribution fits. DPA program details and FHA/conventional pricing are realistic in shape but not tied to a specific snapshot date.
MB-02 covers post-origination distress — modification, forbearance, foreclosure risk. Reach for MB-02 when the loan is in workout, not origination.
MB-03 is non-owner-occupied investor financing on DSCR loans through LLCs. Reach for MB-03 when the property is a rental and the underwriting is property-cashflow rather than borrower-DTI based.
A-01 is the natural next-stage profile — first-home already owned, family formed, mortgage seasoned. Use A-01 when origination is in the past and the file is in servicing.
SL-02 households carry the same DTI-at-limit pressure but driven by IDR student-loan payments rather than housing debt. Use SL-02 when the IDR-payment-as-DTI treatment is the test.
MB-01 — First-Time Homebuyer represents the borrower mid-transaction or freshly post-close on a primary residence purchase: thin liquid reserves, DTI pressed against the QM/ATR 43% ceiling, layered down-payment-assistance programs, and an FHA-versus-conventional product decision driven by PMI/MIP arithmetic. It is the underwriting-edge archetype for origination, TRID, HMDA, and consumer-facing affordability flows.
The 15 shipped MB-01 households have a combined gross income median of $65,639, with a 25th-to-75th-percentile range of $57,278 to $69,021. Median liquid net worth is $42,520 and median total net worth is $132,668 — concentrated in newly originated home equity rather than financial assets.
Yes. The corpus mixes FHA, conventional 97 / HomeReady, and DPA-assisted originations specifically to exercise the product-comparison decision. PMI cancellability on conventional loans versus FHA annual MIP behaviour is a live testing surface in this archetype.
A-01 households already own the home and the loan is seasoned; MB-01 households are mid-transaction or freshly post-close, so origination disclosures, AUS findings, and HMDA reporting are the live surfaces. A-01 is the natural next-stage profile after MB-01's loan completes its first servicing cycle.
Yes — down-payment-assistance second liens, employer-assisted housing, and gifted down payments appear in the household records and should flow through to LE/CD line items, AUS findings, and RESPA Section 8 affiliated-business disclosures in any product testing against this archetype.
No. The shipped v3 corpus is frozen and not regenerable from current code (drift confirmed 2026-05-09). Improvements to first-time-buyer synthesis land in a future v4 with per-archetype golden fixtures in CI to prevent silent drift.
Download households matching this archetype as part of a Wealth Data Set.
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