What Is MBS Pool Number

The MBS pool number is an alphanumeric code that identifies a particular mortgage-backed security (MBS). The MBS pool number is one way to pinpoint a mortgage-backed security when looking for further information. MBS pool numbers are typically six digits in length and are assigned by the issuer according to internal naming conventions. Different issuers such as Freddie Mac, Fannie Mae and Ginnie Mae use different 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. The MBS pool number is sometimes referred to as the MBS series number.

Breaking Down 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.

MBS Pool Numbers Versus CUSIP Numbers

MBS traders favor pool numbers over CUSIP. The CUSIP and the MBS pool number get you to the same place, but 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 on. To get that same information using the CUSIP, you have to go through the extra step of the lookup. 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 mortgage-backed securities 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. Traders can get most of the information they are seeking from this expanded record without diving into disclosure forms. Even just working with the pool number, traders who regularly look at them will be able to distinguish between newer issues and older issues from the same issuer.


Although the MBS pool number and its accompanying prefixes and suffixes can pass on a lot of information as to 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.