GSE product intelligence

Who pools what

• Fannie Mae / Freddie Mac (GSEs) — Buy or swap conventional conforming loans that meet Selling Guide / Seller/Servicer Guide rules, then issue Agency MBS (UMBS for TBA-eligible fixed-rate). Guaranty is the enterprise’s obligation—not the full faith and credit of the U.S. government.
• Ginnie Mae — Does not buy loans or underwrite. Guarantees MBS issued by approved issuers that pool government-insured/guaranteed loans (FHA, VA, USDA/RHS, and certain other HUD programs). Full faith and credit of the U.S.
• Private-label — Non-agency securitizations (no TBA market at Agency scale). Outside this tool’s scope.

UMBS, TBA & specified pools

• UMBS — Uniform MBS: FHFA Single Security so Fannie and Freddie TBA-eligible fixed-rate pools (10/15/20/30-year) are fungible in one TBA market. Re-securitizations of UMBS are called Supers.
• TBA — Trade agrees on term, coupon, face value, price, and settlement; pool number/CUSIP announced ~48 hours before settle (“48-Hour Rule”). SIFMA “good delivery” rules define interchangeable collateral.
• Specified pools — CUSIP known at trade; may command a “pay-up” vs TBA for desirable prepay traits (e.g., small loan size, investor occupancy, geographic concentration).
• Standard vs special — TBA-eligible UMBS typically hold “standard” mortgages; loans with special cash-flow/prepay/tax traits usually go into TBA-ineligible MBS (sometimes de minimis in UMBS).

Pass-through economics

• Borrowers pay note rate → investors receive a lower pass-through (coupon) after servicing fee + guaranty fee (g-fee).
• Investors get a pro-rata share of scheduled P&I plus unscheduled principal (prepayments, curtailments). Fannie Mae fixed-rate certificates typically distribute around the 25th of the month.
• Pass-through / single-class securities vs multiclass (CMOs/tranches) with different payment priorities—Agency CRT programs separately transfer credit risk.

Fannie Mae pooling parameters (summary)

Confirm current Selling Guide Part C3 before delivery—figures below are commonly published guide/capital-markets summaries.

• Single-lender pool — One lender’s loans sharing amortization/term/mortgage type (or ARM plan). Typical minimum aggregate UPB: $1M fixed-rate; $500K ARMs.
• Fannie Majors — Multi-lender pool; once open, a lender may contribute as little as ~$1,000 UPB. Current-production fixed-rate; often ≤12 months seasoning; share of MBS proportional to contribution.
• Note-rate band (fixed-rate) — Loans in a pool generally must have note rates from 25 bp to 112.5 bp above the pool pass-through (e.g., 5.0% coupon → ~5.25%–6.125% notes). Buyups/buydowns can manage excess servicing / coupon fit.
• Term buckets (original term) — Common UMBS-style bands: 30-yr 181–360 mo; 20-yr 181–240; 15-yr 85–180; 10-yr 85–120 (prefixes such as CL/CT/CI/CN; high-balance and high-LTV refi use separate prefixes).
• Ops prerequisites — MBS execution approval + MBS committing access; eligible document custodian + Master Custodial Agreement (Form 2017); deliver data and docs so custodian can certify before pool close / security issuance.
• Execution paths — Lender swap (loans → MBS), portfolio/conduit securitization, structured re-securitizations (including Supers).

Ginnie Mae pooling (summary)

Confirm the current Ginnie Mae MBS Guide and issuer eligibility—not modeled by Analyze.

• Ginnie Mae I — Single-issuer pools (custom). Example: single-family level-payment (suffix SF) often requires a large minimum original principal (commonly cited at $1M for Ginnie I SF).
• Ginnie Mae II — Custom (single issuer) or multiple-issuer pools built from loan packages (smaller packages allowed; MIP rules for buydowns / high-balance mixing apply).
• Pool/loan package types — Level payment, buydown (BD), ARM, graduated payment (GPM), growing equity (GEM), serial notes, and other specialty chapters—each with its own guide chapter and document-custodian rules.
• Issuer bar — Approval + ongoing net worth / liquidity tests (e.g., single-family program: base net worth plus bps of effective outstanding obligations; liquid assets floor). Electronic pooling (e.g., GinnieNET) is required for SF pools.
• Collateral path — Issuer submits pool/loan docs; document custodian certifies (forms such as HUD-11706 / 11711 series) before securities issue.

Ops glossary

ULDD

Uniform Loan Delivery Dataset—loan-level delivery data to GSEs (and related fields such as pooling method on the loan contract).

WAC / WAM

Weighted-average coupon / maturity of loans in the pool—key disclosure stats for investors.

Servicing retained vs released

Whether the seller keeps servicing or transfers it when selling/pooling—affects remittance cycles and economics.

Mandatory commitment

Seller commits to deliver a set amount of loans/MBS by a date; pair with pipeline hedging (often via TBA).

Good delivery

SIFMA rules for what may settle a TBA trade (term, coupon, pool characteristics).

Pool prefix / subtype

Codes describing product, term, high-balance, ARM plan, etc., used for pooling and trading.

First rate change date

First date the ARM note rate can adjust—not the first borrower payment, and usually one month before the first payment change date.

First payment change date

First due date of the new P&I after a rate adjustment (often the 1st of the month after the rate change month).