A TBA, short for “to be announced,” is a type of forward trade used to buy and sell mortgage-backed securities (MBS). What makes it unusual is that the buyer and seller agree on the general terms of the deal, but the specific pools of mortgages that will actually change hands aren’t identified until just before settlement. This mechanism is the backbone of the U.S. mortgage market, handling trillions of dollars in trading volume each year and directly influencing the interest rates homebuyers see when they apply for a mortgage.
How a TBA Trade Works
When two parties enter a TBA trade, they lock in six parameters: the coupon rate, the maturity date, the issuer (such as Fannie Mae or Freddie Mac), the settlement date, the face value of the securities, and the price. Everything else remains open. The buyer doesn’t know which specific mortgage pools they’ll receive, and the seller hasn’t committed to delivering any particular ones.
Forty-eight hours before the settlement date, the seller notifies the buyer which specific MBS will be delivered. This is called the “pool notification” step. Until that point, the trade exists purely as a contract defined by those six parameters. The Securities Industry and Financial Markets Association (SIFMA) maintains a Uniform Practices Manual that governs the notification process, settlement dates, and other operational details of TBA trading.
Why the TBA Market Exists
Individual mortgage-backed securities are unique. Each pool contains a different mix of loans with varying balances, borrower credit profiles, and geographic locations. If every MBS trade required the buyer to evaluate the exact pool beforehand, trading would be slow, expensive, and illiquid. The TBA structure solves this by treating MBS with similar characteristics as interchangeable. A Fannie Mae 30-year security with a 5% coupon is considered fungible with any other Fannie Mae 30-year security carrying the same coupon, at least for trading purposes.
This fungibility creates enormous liquidity. Lenders can sell their newly originated loans into the TBA market almost immediately, which frees up capital to make more loans. That liquidity is a big reason U.S. mortgage rates stay relatively low compared to housing markets in countries without a similar structure. When a lender locks in your mortgage rate, they’re often hedging that commitment with a TBA trade on the same day.
What Makes a Security TBA-Eligible
Not every mortgage-backed security qualifies for TBA trading. To be considered TBA-eligible, a security must be issued by one of the government-sponsored enterprises (Fannie Mae or Freddie Mac) and meet standardized characteristics that make it interchangeable with similar securities. The introduction of the Uniform Mortgage-Backed Security, or UMBS, was designed to make this easier. A UMBS is a single-class MBS backed by fixed-rate loans on single-family properties, and it carries the same features (payment delay, pooling structure, minimum pool size) regardless of whether Fannie Mae or Freddie Mac issued it.
The Federal Housing Finance Agency (FHFA) oversees this alignment between the two enterprises. If prepayment speeds between Fannie Mae and Freddie Mac pools diverge too much, the securities stop being truly interchangeable, which could fragment the market. FHFA defines a misalignment as a difference of 2 percentage points or more in the three-month conditional prepayment rate between comparable groups of securities, and it has authority to require the enterprises to adjust their programs if divergence becomes a problem.
Specified Pools: The Alternative to TBA
Some investors don’t want the uncertainty of a TBA trade. They want to choose exactly which mortgage pools they’re buying, often because those pools have characteristics that make them more or less likely to prepay quickly. These are called specified pool trades.
Specified pools are defined by features like a maximum loan size of $200,000, a minimum loan-to-value ratio of 80% at origination, or a maximum borrower credit score of 700. Pools backed entirely by investor-owned properties or properties in certain states also qualify. Investors pay a premium for these pools because the loan characteristics give them more predictable cash flows. A pool of smaller loans, for example, tends to prepay more slowly because those borrowers are less likely to refinance.
Dollar Rolls: Extending TBA Positions
A dollar roll is a common transaction built on top of the TBA market. It works like a short-term financing arrangement. You sell a TBA position for the current month’s settlement and simultaneously agree to buy back a similar position for a future month’s settlement. The securities you get back won’t be the same pools you sold, but they’ll have the same coupon and maturity.
The practical effect is that you receive cash now and defer delivery to a later date. During the gap, you can invest that cash elsewhere. The price difference between the two legs of the trade, sometimes called the “drop,” reflects the cost of this implied financing. When the drop is unusually favorable, traders say the roll is “on special.” The most common dollar rolls use one-month and three-month intervals. Dollar rolls let investors extend their positions without taking on additional duration risk, which makes them a flexible tool for managing mortgage portfolios.
Why TBA Trading Matters to Borrowers
If you’re a homebuyer, you’ll never interact with the TBA market directly, but it shapes your experience in important ways. The liquidity TBA trading provides is what allows lenders to offer rate locks weeks or even months before closing. Without a deep, liquid forward market for mortgage securities, lenders would face much more risk in committing to a rate, and they’d charge you for that risk through higher rates or wider spreads.
The TBA market also helps keep the spread between mortgage rates and Treasury yields relatively tight. Because lenders know they can sell their loans efficiently into the secondary market, they don’t need to hold as much capital against those loans or demand as large a profit margin on each one. That efficiency flows through to you as a lower rate on your mortgage.