MBS Pool Number

What Is an MBS Pool Number?

An MBS pool number is an alphanumeric code used to identify a particular mortgage-backed security (MBS), which is a type of asset-backed security that is also sometimes called a mortgage-related security or mortgage pass-through.

The MBS pool number is one way to pinpoint and unearth further information on these types of investments, which consist of home loans that are sold by the issuing banks to a government-sponsored enterprise (GSE) or a financial company and then bundled together to form a single investable security. The securities issued represent claims on the principal and interest payments made by borrowers on the loans that are in the pool.

MBS pool numbers are typically six digits in length and are assigned by the issuer according to internal naming conventions. The MBS pool number is sometimes referred to as the MBS series number.

Understanding an MBS Pool Number

MBS pool numbers are simply a label that distinguishes one MBS from another. Issuers use specific naming conventions, so MBS traders learn to identify the issuer from the pool number. This is a critical skill for research, as you can then jump directly to the issuer's pool number lookup system to access disclosures related to that MBS.

Different issuers, such as Freddie Mac, Fannie Mae, and Ginnie Mae, use contrasting alpha characters as the initial digit in their MBS pool numbers to identify the pool as their issue. For example, a Freddie Mac 30-year pool number might be D54321 while a Fannie Mae 30-year pool number might be F54321.

MBS Pool Numbers vs. CUSIP Numbers

MBS traders favor pool numbers over CUSIP, a nine-digit alphanumeric number assigned to all securities approved for trading in the United States and Canada by the Committee on Uniform Securities Identification.

The CUSIP and the MBS pool number get you to the same place, though the latter offers more immediate details. The MBS pool number is part of a pseudo-ticker that includes an identifier of the issuer, the pool type, the issue date, the issuer ID, and so forth. To get that same information using the CUSIP, you have to go through an extra step of the lookup process. 

Special Considerations

When traders refer to the pool number, they are often speaking about the larger pool record that includes all the information, rather than the specific six-digit identifier. Regular issuers of MBSs have set up naming conventions with suffixes and prefixes that show whether an MBS is a single-family loan pool, construction loan pool, and so on.

Although the MBS pool number and its accompanying prefixes and suffixes can pass on a lot of information regarding the type and character of the security, investors need to go to the lookup pages that are usually hosted on the issuers' websites to get into the details.

These lookup pages will generally accept either the CUSIP number or the pool number. Once that is provided, investors can access historical information on coupons, detailed information on the stratification of the issue into tranches, loan-level information on the borrowers, interest adjustment dates, and much more.