CFA Level I Exam · Mortgage-Backed Security (MBS) Instrument and Market Features

Commercial Mortgage-Backed Securities (CMBS) for CFA Level I

Updated 7 October 2026 · Fact-checked

A CMBS is a security backed by a pool of loans on income-producing commercial property. Loans are usually non-recourse, so you analyze each property's cash flow. Key metrics are DSCR (net operating income ÷ debt service) and LTV (loan ÷ property value). Call protection is stronger than in RMBS, but balloon risk is higher.

Understand Commercial Mortgage-Backed Securities (CMBS)

A commercial mortgage-backed security (CMBS) is a bond backed by commercial mortgage loans. The loans finance income-producing property such as offices, shopping centers, apartment blocks, hotels and warehouses. Interest and principal from the loans flow to CMBS investors, split into tranches by seniority.

The big difference from residential MBS (RMBS) is where the repayment comes from. A home loan is repaid from the borrower's salary. A commercial loan is repaid from the net operating income (NOI) the property earns. So you analyze the property, not the person. Commercial loans are typically non-recourse: if the borrower defaults, the lender can take the property but cannot pursue the borrower's other assets. The property is the only real security.

Because of this, CMBS analysis is done at the loan level. Each loan is judged on its own property, using DSCR and LTV. RMBS is analyzed at the pool level, because thousands of small, similar loans behave statistically. A CMBS pool has relatively few large, different loans, so one bad loan matters.

Prepayment behaves differently too. Commercial loans usually have call protection. This can be a prepayment lockout (no prepayment for a period), defeasance (the borrower replaces the loan's collateral with a portfolio of securities that covers the remaining payments), prepayment penalty points, or yield maintenance charges. Call protection comes at both the loan level and the structure level. Structure-level call protection comes from the sequential-pay structure, because prepayments go to the most senior tranche first. Subordination is different: it is credit enhancement, which protects senior tranches against losses, not against prepayment. As a result, CMBS investors face far less prepayment risk than RMBS investors.

The trade-off is balloon risk. Many commercial loans amortize over a long period but mature much sooner, leaving a large final (balloon) payment. If the borrower cannot refinance at maturity, the loan may default or be extended. This is also called extension risk for investors, because the cash flows arrive later than expected. Balloon risk is greater when interest rates are high or property values have fallen, because refinancing is harder.

Key formulas to remember

Debt service coverage ratio (DSCR): DSCR = Net operating income ÷ Debt service; Debt service is the scheduled interest plus principal payments. Higher is safer. A DSCR below 1.0 means NOI does not cover the payments.
Loan-to-value ratio (LTV): LTV = Loan amount ÷ Appraised property value; Lower is safer. A lower LTV gives the lender a larger equity cushion if the property is sold.
Net operating income (NOI): NOI = Rental income and other property income − Operating expenses; NOI is before debt service, depreciation and income taxes.
Loan-level vs pool-level: CMBS: loan-level analysis; RMBS: pool-level analysis; Commercial pools hold few, large, dissimilar loans. Residential pools hold many small, similar loans.
Balloon payment: Balloon = Remaining balance due at loan maturity; Risk is that the borrower cannot refinance. For investors this shows up as extension risk and default risk.

How to solve Commercial Mortgage-Backed Securities (CMBS) questions

Use this approach for any CMBS question, whether it is conceptual or numerical.

1Identify whether the question is about a commercial loan (property cash flow, non-recourse) or a residential loan (borrower credit, prepayment).
2Decide the level of analysis. Few large loans means loan-level; many small loans means pool-level.
3If numbers are given, compute NOI first, then debt service, then DSCR = NOI ÷ debt service.
4Compute LTV = loan ÷ property value. Check which direction is safer: higher DSCR, lower LTV.
5For prepayment questions, look for call protection: lockout, defeasance, prepayment penalties, yield maintenance, or the sequential-pay structure. Do not count subordination here, because it is credit enhancement.
6For maturity questions, look for a balloon payment and think refinancing risk and extension risk.
7Eliminate the two wrong options by checking direction (safer or riskier) and which security type (CMBS or RMBS) each option describes.
8Re-read the stem to confirm the ratio asked for and the units.

Quickest way: Direction-and-type check

When to use it: Use for conceptual questions where you have about 90 seconds and can decide by logic instead of calculating.

Ask: is this CMBS or RMBS? CMBS means property cash flow, non-recourse, loan-level, call protection, balloon risk.
Ask: is the statement about risk going up or down? Higher DSCR and lower LTV mean lower credit risk.
Remember the pairing: CMBS has low prepayment risk but higher balloon and extension risk; RMBS has high prepayment risk.
Cross out any option that gives CMBS the RMBS features, then pick the one left.

Common mistakes in Commercial Mortgage-Backed Securities (CMBS)

Saying CMBS prepayment risk is high like RMBS.
Students assume all mortgage securities prepay when rates fall.
Fix: Remember commercial loans carry call protection (lockouts, defeasance, penalties, yield maintenance). Prepayment risk is much lower than in RMBS.
Treating a higher LTV as safer.
Students mix up the direction of the ratio with DSCR, where higher is better.
Fix: LTV is loan over value. A bigger loan relative to value means a thinner equity cushion, so it is riskier. Lower LTV is safer.
Using total income instead of NOI in DSCR.
Students forget to subtract operating expenses.
Fix: Always compute NOI = income − operating expenses before dividing by debt service.
Assuming the lender can claim the borrower's other assets after default.
Residential loans are often thought of as full-recourse.
Fix: Commercial loans are typically non-recourse. The lender's claim is limited to the property, which is why property-level analysis matters.
Confusing balloon risk with prepayment risk.
Both relate to when principal comes back.
Fix: Prepayment risk is principal returned early. Balloon risk is a large payment at maturity that the borrower may be unable to refinance, which leads to default or extension.
Using pool-level statistics for a CMBS pool.
Students carry over the RMBS approach.
Fix: CMBS pools have few large, different loans, so each loan is analyzed by its own DSCR and LTV.

Worked examples

Example 1

A shopping center generates rental income of $5,000,000 a year and has operating expenses of $1,800,000. The annual debt service on its mortgage is $2,000,000. What is the DSCR? A. 1.40, B. 1.60, C. 2.50.

Show the solution

NOI = 5,000,000 − 1,800,000 = 3,200,000.
DSCR = 3,200,000 ÷ 2,000,000 = 1.60.
Option A (1.40) is wrong because it would need NOI of 2,800,000. Option C (2.50) would come from using revenue ÷ debt service (5,000,000 ÷ 2,000,000) and ignoring expenses.

Answer: B. DSCR is 1.60.

Example 2

A commercial mortgage loan of $24,000,000 is secured by a property appraised at $40,000,000. What is the loan-to-value ratio? A. 40%, B. 60%, C. 167%.

Show the solution

LTV = loan amount ÷ appraised property value.
LTV = 24,000,000 ÷ 40,000,000 = 0.60, or 60%.
Option A (40%) is the equity cushion (1 − 0.60), not the LTV. Option C (about 167%) comes from inverting the ratio (40,000,000 ÷ 24,000,000).

Answer: B. LTV is 60%.

Example 3

Which statement about CMBS compared with RMBS is most accurate? A. CMBS pools are best analyzed at the pool level because they contain thousands of similar loans. B. CMBS investors generally face less prepayment risk because commercial loans typically have call protection. C. CMBS loans are typically full-recourse, so borrower credit is the main concern.

Show the solution

Option A describes RMBS. CMBS pools hold few, large, different loans and are analyzed loan by loan.
Option C is wrong because commercial mortgage loans are typically non-recourse, so the property's cash flow matters most.
Option B is correct. Lockouts, defeasance, prepayment penalties and yield maintenance reduce prepayment risk. The trade-off is balloon risk.

Answer: B.

Exam tips

Memorize the CMBS profile in one line: loan-level, non-recourse, call-protected, balloon risk, judged by DSCR and LTV.
For ratio questions, check direction first. Higher DSCR and lower LTV are safer. This alone often eliminates two options.
Compute NOI before DSCR. A wrong-option trap often uses gross income instead of NOI.
When a stem mentions refinancing at maturity, think balloon risk and extension risk, not prepayment risk.
Numerical options are listed smallest to largest. If you forget expenses, your DSCR will be too high, so check that you subtracted operating expenses to get NOI.

Practice questions from Mortgage-Backed Security (MBS) Instrument and Market Features

Commercial Mortgage-Backed Securities (CMBS): frequently asked questions

What is the main difference between RMBS and CMBS?

RMBS is backed by many small home loans, usually analyzed at the pool level, with high prepayment risk. CMBS is backed by fewer large loans on income-producing property, analyzed at the loan level, with call protection and balloon risk. CMBS loans are typically non-recourse.

How do you calculate DSCR for a CMBS loan?

Divide the property's net operating income by its scheduled debt service (interest plus principal). A DSCR above 1.0 means NOI covers the payments. A higher value gives the lender a larger safety margin.

What does non-recourse mean in commercial mortgages?

If the borrower defaults, the lender can seize the property but cannot claim the borrower's other assets. This is why lenders focus on the property's cash flow and value through DSCR and LTV.

What is balloon risk and how does it differ from call protection?

Balloon risk is the chance the borrower cannot refinance the large final payment at maturity, which can cause default or extension. Call protection limits early repayment (prepayment). One concerns the end of the loan and the other concerns early repayment.