Identified MBS pool traded or analyzed for known collateral traits rather than only generic TBA terms.
A specified pool is an identified mortgage-backed-security pool traded or analyzed for its known collateral characteristics rather than only as an interchangeable generic TBA position.
Specified pools matter because two securities with the same agency, term, and coupon can still have different expected prepayment behavior. Investors may pay more for a named pool whose loan sizes, geography, seasoning, occupancy mix, or other disclosed traits are expected to produce more desirable cash flows.
That extra value over a generic TBA price is commonly called a pay-up. A pay-up is not added to an individual borrower’s principal balance; it is a secondary-market price difference for the security.
Specified pools also show the limit of TBA interchangeability. Standardization supports a liquid forward market, but actual collateral can still matter once investors compare identified securities.
Borrowers rarely see specified-pool language directly. It appears after loans close, when eligible mortgages are pooled, disclosed, delivered, traded, or analyzed in the secondary market.
The term becomes practical when explaining how loan-level characteristics can affect lender execution even after broad product and coupon requirements are met. Those effects can influence rate-sheet adjustments, but the eventual pool trade does not rewrite the borrower’s note.
| Pool characteristic | Why it can matter |
|---|---|
| Original loan-balance range | Smaller balances can reduce the economic incentive to refinance |
| Geography | Taxes, housing turnover, and refinance behavior can differ by location |
| Loan age and pool factor | Seasoning and remaining principal help frame expected cash-flow timing |
| Occupancy or property mix | Borrower behavior can differ across owner-occupied, second-home, and investor loans |
| WAC and coupon spread | Mortgage rates relative to the security coupon help describe refinance incentive |
These are analytical categories, not promises. Borrowers in any identified pool can still sell, refinance, curtail principal, or default, and actual results can differ from an investor’s expectation.
| Market label | What it tells the reader |
|---|---|
| To-Be-Announced Market | Broad agency MBS trade before exact pools are named |
| Specified-pool trade | Known pool valued for its disclosed collateral characteristics |
| Mortgage Pool | Group of loans behind a security |
| Pool Factor | How much of the original pool balance remains |
A generic TBA security is quoted at 100.50, while an identified pool with collateral characteristics expected to prepay more slowly is quoted at 100.75. The 0.25-point difference is the simplified pay-up.
On $2 million of current principal, that difference equals $5,000. The investor is paying for expected cash-flow behavior, not changing any borrower’s rate or balance.
Specified pool differs from Mortgage Pool because every MBS pool is a group of loans, while specified pool emphasizes trading or analysis based on a known pool’s actual disclosed traits.
It differs from the To-Be-Announced Market because a TBA trade is agreed before exact pools are known. Every settling TBA trade eventually receives identified pools, but that routine allocation is not automatically a specified-pool investment strategy.
It also differs from MBS Price because specified pool is the identified collateral pool, while MBS price is the market value at which the security or pool trades.