Stated annual rate used to calculate investor interest on a mortgage-backed security.
An MBS coupon is the stated annual rate used to calculate interest paid on a mortgage-backed security’s outstanding principal balance.
MBS coupon matters because agency MBS prices and trades are organized partly by security coupon. A 5.5% MBS and a 6.0% MBS represent different investor cash-flow rates and can trade at different prices even when they share the same agency and term.
The security coupon is not the rate on one borrower’s note. Mortgage interest from the underlying loans must also support servicing compensation, guaranty fees, and any other applicable deductions before security interest reaches investors.
In many fixed-rate agency pass-through securities, MBS coupon and pass-through rate refer to the same stated rate. Market participants often say coupon when discussing trading and pass-through rate when emphasizing cash-flow calculation.
Borrowers usually encounter the concept indirectly when learning why mortgage rates move during the day, why rate sheets can reprice before lock, or why a lender groups closed loans by investor delivery requirements.
The term becomes practical when separating a borrower’s Note Rate from the investor-facing rate on a Mortgage-Backed Security (MBS). The borrower’s note rate does not change when the loan is placed into a security with a particular coupon.
| Cash-flow layer | What the rate describes |
|---|---|
| Borrower note rate | Contractual interest rate on one mortgage |
| Weighted Average Coupon | Current-balance-weighted note rates across the pool |
| Servicing and guaranty components | Amounts supporting account administration and applicable credit guarantees |
| MBS coupon or pass-through rate | Stated rate used to calculate investor interest on security principal |
For fixed-rate agency pools, eligibility rules control which note rates can support a given security coupon. The relationship is therefore governed by pooling and fee requirements, not by casually rounding a borrower’s rate to the nearest MBS coupon.
| Term | What it describes |
|---|---|
| Note Rate | Interest rate written into the borrower’s note |
| MBS coupon | Stated cash-flow rate on the security |
| Current Coupon | Theoretical coupon estimated to trade near par |
| MBS Price | Quoted market value for a security coupon and settlement |
| Pass-Through Rate | Rate passed through to investors after certain deductions |
| Guaranty Fee | Fee connected to agency credit support |
A simplified pool has a 6.25% weighted mortgage rate. If servicing and guaranty components total 0.75 percentage points, the investor-facing coupon may be 5.50%, subject to the actual pooling rules and loan-level spreads.
A borrower in that pool might have a 6.375% note rate while another has 6.125%. Each borrower continues paying the rate in the individual note; investors receive interest calculated using the security’s stated coupon.
MBS coupon differs from Note Rate because the note rate belongs to the borrower loan, while the MBS coupon belongs to the security.
It differs from Pass-Through Rate mainly in emphasis. In many fixed-rate pass-through MBS, the two terms identify the same rate; coupon is the trading label, while pass-through rate emphasizes the investor-interest calculation.
It differs from Current Coupon because an MBS coupon is stated on an actual security, while current coupon is an estimated market reference rate near par.
It also differs from Mortgage Rate Sheet because the rate sheet is the lender pricing grid, while MBS coupon is a market/security term that can influence that grid.