Agency securities, asset-backed and mortgage-backed securities

Follow the collateral and the promise

Agency securities connect investors with government agencies or government-sponsored enterprises. The word agency does not establish identical federal backing. Ginnie Mae, the Government National Mortgage Association, guarantees timely principal and interest on qualifying mortgage-backed securities issued by approved issuers. Its guarantee carries the full faith and credit of the United States. Fannie Mae and Freddie Mac are government-sponsored enterprises; their securities do not carry that same full faith and credit guarantee. Federal support and a federal guarantee are different concepts.

Assets generate the payments

An asset-backed security, or ABS, relies primarily on cash flow from financial assets such as loans, leases, or receivables. Auto loans and credit-card receivables are common examples. A mortgage-backed security, or MBS, uses mortgage loans as collateral. Mortgage-backed securities are part of the broader asset-backed family, although market terminology often separates mortgage products from other ABS.

A mortgage pass-through pools mortgages and passes principal and interest through to investors after applicable fees. Payments commonly arrive monthly. Principal includes scheduled repayments and any additional principal paid early. Unlike a conventional bond that returns principal at maturity, a pass-through generally returns principal over time, reducing its outstanding balance.

Timing creates risk

When interest rates fall, homeowners have more incentive to refinance. Faster repayments create prepayment risk: investors receive principal earlier than expected and may have to reinvest at lower rates. Faster prepayments can also hurt an investor who paid a premium, because principal is repaid at par rather than at the investor's premium purchase price.

When rates rise, refinancing tends to slow. Principal may remain outstanding longer than expected, creating extension risk. Investors retain older, lower-rate cash flows while market yields are higher; the security's price can fall. Average life estimates when principal is expected to return, weighted by the amounts repaid. It changes with prepayment assumptions and is different from final maturity.

CMOs divide the cash flow

A collateralized mortgage obligation, or CMO, divides mortgage cash flows into classes called tranches. In a simple sequential-pay structure, principal goes to the first tranche until it is retired, then to the next. Different tranches therefore have different expected payment timing and risk exposure. Structuring redistributes prepayment and extension risk rather than eliminating it. Payment priorities depend on the structure.

A payment guarantee addresses the promised payments; it does not protect a resale price or eliminate changing cash-flow timing. These distinctions describe products and risks, not a recommendation to invest.