MBS TBA vs. Specified Pools: What Is Known Before Delivery?

TBA means “to be announced.” In the U.S. agency mortgage market, it describes a forward trade for a defined category of mortgage-backed securities (MBS) whose exact mortgage pool and CUSIP are disclosed later. It does not mean the buyer is agreeing to an unspecified price or to any mortgage bond the seller chooses. The parties set the trade terms first; the pool information follows under market notification rules.

The contract and the security are different things. An MBS is backed by mortgages already assembled into a security. A TBA is the agreement to exchange securities of a stated type on a future settlement date. SIFMA defines a delayed-delivery contract as a future MBS purchase or sale for which some pool information has not yet been identified to the buyer. The association describes the market as a way to trade forward MBS issued by Fannie Mae, Freddie Mac, and Ginnie Mae. The detailed TBA product and delivery standards depend on the agency, term, coupon, and governing market rules. This guide focuses on U.S. single-family agency pass-throughs and the Uniform Mortgage-Backed Securities (UMBS) market; private-label securities and collateralized mortgage obligation (CMO) tranches follow different structures. See SIFMA’s common MBS market terms and TBA market governance and Uniform Practices Manual.

“To be announced” is therefore a timing feature of the trade, not a promise that the underlying mortgages will be created from scratch after the trade. A seller may already have eligible securities available, may be assembling a deliverable pool, or may expect to produce securities from mortgage loans. What remains open is the pool identity within the contract’s permitted delivery set.

At trade time, the buyer and seller establish the product or agency category, mortgage term, coupon, face amount, dollar price, and settlement date. The exact pool number and CUSIP are generally left for later notification. For TBA-eligible UMBS, Fannie Mae describes the trade as fixing the maturity, coupon, face value, price, and settlement date while leaving the pool number and CUSIP undisclosed until the 48-hour day. The full trade confirmation and applicable conventions determine the precise terms.

For a simplified price illustration, suppose a buyer agrees to receive $1,000,000 face amount at 99.50 per $100 of face. Multiplying $1,000,000 by 0.995 gives $995,000 before settlement adjustments and transaction costs. That calculation describes the agreed price convention; it does not identify the pool, predict its later cash flows, or represent a live quote.

The open CUSIP is not a blank cheque. A TBA contract is tied to a standard product description and delivery conditions. If two tickets differ in agency, term, coupon, amount, price, or settlement date, they are not made equivalent just because both are called “TBA.” Confirm the full description rather than relying on a desk shorthand such as “30-year” or “current coupon.”

The market can trade a broad class of pools before choosing the final CUSIP because only securities that satisfy defined delivery standards can be allocated to the contract. SIFMA’s Uniform Practices Manual sets out notification, settlement, and “good delivery” guidance. The rules address matters such as the product delivered, pool information, face amount, timing, and settlement process. Counterparties can also negotiate terms for a particular transaction, so a summary of standard practice is not a substitute for the actual confirmation.

These rules support a practical homogeneity assumption: within the contract’s delivery criteria, eligible pools can be treated as sufficiently comparable to trade against one standard price. Fannie Mae and Freddie Mac UMBS, for example, were standardized so either enterprise’s qualifying UMBS can be delivered into the unified TBA market under the applicable terms. The standardization helps create liquidity across many underlying mortgage loans.

Comparable for delivery does not mean identical as an investment. Two pools with the same stated term and coupon can differ in borrower balances, geography, occupancy, loan age, and other collateral details. Those details can affect prepayments and projected cash flows. Good delivery establishes whether securities meet transaction rules; it does not certify equal credit, market, liquidity, or prepayment risk. See SIFMA’s current Chapter 8 good-delivery guidelines and Freddie Mac’s explanation of TBA-eligible and special-characteristic mortgages.

“TBA-eligible” and “TBA trade” also name different things. TBA eligibility describes a security that can meet the delivery criteria for a relevant TBA contract. A TBA trade is the agreement made between counterparties. A specified pool may be eligible for delivery into a matching TBA, while another identified pool may be outside the eligible set. Check the security and contract terms rather than assuming every agency MBS can be delivered into every TBA.

The “48-hour day” is the scheduled point before settlement when the seller provides the buyer with the pool or group information needed to identify the securities. SIFMA’s 48-Hour Rule frames the notice around the business day before the agreed settlement and the applicable cutoff. It is not a general instruction to count any 48 clock hours backward. The precise notification details and cutoff depend on the transaction’s market practice, communication channel, counterparties, and any current extension or disruption notice.

After notification, the buyer can compare the delivered pool information with the trade description and delivery requirements. The seller still has to deliver in good form on the settlement date, and the buyer still has to fund the trade according to its terms. A late or incomplete notification can affect whether delivery is timely; exact remedies and timing depend on the governing practices and agreement. Read SIFMA’s pool notification chapter together with the current manual and trade confirmation.

MBS notification and settlement dates are published on a class-specific calendar. Different product classes do not necessarily share the same settlement date in a month, and weekends and holidays affect the schedule. A trader looking at a “48-hour day” should first identify the contract’s class and settlement date, then use the corresponding notice date and cutoff. SIFMA maintains the current MBS notification and settlement calendar; do not reuse a date from a prior year or another class.

The sequence is easier to follow as three separate events: agree on the TBA terms, receive the required pool information by the applicable notice deadline, then exchange securities and funds on settlement. The middle event identifies what will satisfy the delivery obligation; it does not renegotiate the original price each time the market moves.

In a specified-pool trade, the pool number and CUSIP are known when the parties agree to the transaction. The buyer can evaluate the identified collateral before committing to the price. In a TBA trade, the buyer instead accepts a class of securities that must meet the contract’s delivery rules, with the actual pool named later. Fannie Mae’s MBS trading overview describes this distinction and explains that specified pools with additional collateral value may trade at a different price from a comparable TBA.

“Specified pool” does not automatically mean “TBA-ineligible.” A pool with an identified CUSIP may still meet the delivery criteria for a matching TBA. In that case, a seller might deliver it against an open TBA, or the parties might negotiate a specified-pool trade that commits to that security from the start. Some securities with unusual collateral characteristics may not be eligible for TBA delivery at all. The exact relationship depends on product and contract rules.

The choice changes what the buyer knows at execution. A TBA offers exposure to a standardized delivery category without selecting one pool. A specified trade gives the buyer certainty about pool identity, but that certainty can come with a price difference, lower liquidity, or a need to assess pool-level data. Neither label tells you whether a trade is suitable; they describe how the deliverable is identified and priced.

Some investors value a pool’s collateral features because they expect those features to change prepayment behavior or cash-flow stability. A pool made up of particular borrower or property groups may be worth more to a buyer than the broad TBA delivery class. If so, dealers may quote a “pay-up”: an additional price over a comparable TBA dollar price. Fannie Mae lists investor-property loans, smaller loan balances, and geographic concentration among examples of characteristics seen in specified pools. Those examples are not a universal ranking, and market values can change.

Consider a purely hypothetical $1,000,000 face trade. If a comparable TBA is quoted at 99.50 and a specified pool carries a 0.25-point pay-up, its illustrative price is 99.75. At one-quarter of one percent of face, that price difference equals $2,500 before settlement adjustments and costs. The example explains the arithmetic only. It is not a quote, a forecast of a pool’s performance, or proof that the specified security will outperform.

A pay-up is not a separate coupon or guaranteed extra return. It is a higher purchase price for a pool whose characteristics the market values at that time. If prepayments differ from expectations, mortgage rates move, or the pool becomes harder to sell, the realized value may not match the buyer’s original rationale. To assess the rate-sensitivity side of that risk, see why bond-fund prices can fall when rates rise and the guide to bond duration and convexity.

A lender may agree to sell agency MBS forward while it is still originating and closing mortgage loans. A TBA price can help the lender manage changes in secondary-market prices before the final loan pool is assembled. Fannie Mae describes lenders as using TBA securities to hedge mortgage pipelines; dealers and investors use them for several other financing and portfolio purposes. The standardized contract makes it possible to trade a larger market than if every trade required the pool CUSIP at the outset.

The hedge remains imperfect because the future loans and the delivered pool are not known with certainty. Some borrowers may not close, loans may not meet the planned pooling requirements, and the characteristics of the final pool can differ from the broad TBA class. The price of the TBA and the price of a particular pool can also move differently. This leaves pipeline fallout, basis, prepayment, and delivery risks even when the lender has an offsetting TBA position.

A TBA contract also does not lock a borrower’s mortgage rate by itself. A mortgage offer, rate lock, lender pricing, loan eligibility, fees, and the lender’s hedge policy are separate parts of the transaction. The MBS market can influence mortgage economics, but a change in one TBA quote does not translate mechanically into the same change in every retail loan offer.

For investors, the same distinction matters when interpreting a hedge. A position in a TBA may offset some broad agency-MBS price exposure, but it does not necessarily offset the prepayment profile or liquidity of a particular pool. A hedge ratio based only on face value can miss differences in duration, coupon, settlement timing, and collateral. The contract may reduce one exposure while leaving others in place.

Start with the trade confirmation. Verify the agency or product category, mortgage term, coupon, face amount, agreed dollar price, settlement date, and whether the contract is TBA or pool-specific. Then confirm the pool or CUSIP if already allocated, the original and current face conventions, and whether the security satisfies the applicable delivery requirements. Product labels and desk shorthand are not enough to settle a discrepancy.

Next, distinguish the trade price from the value of the eventual mortgage cash flows. Check the current pool factor and disclosed collateral information where available. Compare any specified-pool pay-up with the TBA price for the matching term and coupon, and ask which pool feature supports the difference. A price premium may reflect expected prepayment behavior or scarcity, but it does not establish a realized return advantage.

Finally, check the class-specific notification and settlement dates, the applicable pool-notification cutoff, funding arrangements, and any current operational notice. Do not assume that all mortgage products use one monthly date or that the nominal 48-hour rule means the same cutoff in every trade. Use the current SIFMA Uniform Practices Manual and the parties’ confirmation for operational questions.

The useful distinction is simple: a TBA trade fixes the category, price, and settlement terms before the exact pool is named; a specified-pool trade names that security at execution. Delivery rules connect the two markets, while collateral differences, prepayment behavior, liquidity, and settlement mechanics remain relevant. This guide explains U.S. agency MBS conventions, not the terms of every contract or a recommendation to trade.