CMBS primer: how commercial mortgage-backed securities work

A CMBS (commercial mortgage-backed security) is a bond paid from a pool of commercial real estate loans held in a trust. Borrowers’ monthly payments pass to bondholders by seniority: the top classes are paid first and the bottom classes lose first. One real deal, BANK5 2025-5YR14, pooled 25 loans on 72 properties ($884,437,753) and issued 16 classes of certificates.

The rest of this primer follows that one deal, using its prospectus and pooling and servicing agreement, both filed with the SEC on April 2, 2025. Other deals use similar but not identical terms.

CMBS in four sentences

1. A lender makes a fixed-rate loan on a stabilized commercial property, intending to sell it.
2. Several lenders sell their loans to a depositor, which places them in a trust that elects REMIC tax status.
3. The trust issues classes of certificates (the bonds), from AAA-rated senior classes down to an unrated first-loss class.
4. Servicers collect the payments and manage the loans for the life of the trust under one contract, the pooling and servicing agreement.

Who does what: the parties in a real deal

Role	What it does	In BANK5 2025-5YR14
Sponsors and loan sellers	Originate the loans and sell them into the deal; give representations and warranties on each loan	Wells Fargo Bank, Morgan Stanley Mortgage Capital Holdings, JPMorgan Chase Bank, Bank of America
Depositor	Buys the loans and deposits them into the trust; registers the offering with the SEC	Wells Fargo Commercial Mortgage Securities, Inc.
Issuing entity (trust)	Holds the loans for bondholders; a New York common law trust here	BANK5 2025-5YR14
Master servicer	Collects payments, handles routine requests, advances missed payments	Trimont LLC (Midland Loan Services as primary servicer on some loans)
Special servicer	Takes over loans in default or imminent default; works them out or liquidates	Torchlight Loan Services, LLC
Trustee	Holds the mortgages of record for the trust	Computershare Trust Company, N.A.
Certificate administrator	Calculates and pays distributions, publishes reports, acts as REMIC administrator	Computershare Trust Company, N.A.
Operating advisor	Reviews the special servicer’s work for bondholders	BellOak, LLC
Asset representations reviewer	Reviews delinquent loans for breaches of the loan sellers’ representations when investors vote for it	BellOak, LLC
Directing certificateholder	Represents the controlling (most junior) class; consents to major servicing decisions	Torchlight Investors, LLC (initially)
B-piece buyer	Buys the first-loss classes and holds them to satisfy risk retention	TL DF8 RR, LLC, a Torchlight affiliate
Rating agencies	Rate the offered classes	Fitch, KBRA and Moody’s

The overlap in the last rows is normal, and it matters to a borrower: the same investor group that holds the first-loss bonds chose the special servicer and controls major decisions. More on that on the B-piece and master vs special servicer pages.

How the money moves each month

Borrowers pay the master servicer. The certificate administrator distributes to bondholders on the fourth business day after the determination date, the 11th of each month (BANK5 2025-5YR14 prospectus, “Distributions”). Interest goes to the senior classes first, then principal to the senior classes in sequence, then down the stack. Losses are allocated the other way, starting with the bottom class. The full order, with the real class sizes, is on CMBS tranches.

If a borrower misses a payment, the master servicer generally advances it to bondholders (principal and interest advances), unless it judges the advance unrecoverable. It does not advance a missed balloon payment. That advancing is why a short delinquency does not immediately hit the bonds, and why servicers act quickly when a loan stops paying. The day-by-day sequence is on the servicer clock.

Kinds of CMBS

Type	What is in the pool	Notes
Conduit (multi-borrower)	Dozens of loans from several lenders, many property types	The classic CMBS deal; BANK5 2025-5YR14 is one. See conduit loans.
Single-asset, single-borrower (SASB)	One large loan, or a portfolio of one sponsor	Bonds depend on one property or sponsor. See SASB loans.
Agency CMBS	Multifamily loans guaranteed by Fannie Mae, Freddie Mac or Ginnie Mae	A separate market; see CMBS vs agency loans.
CRE CLO	Floating-rate loans on transitional properties	A related market with its own structure; compare CMBS vs bridge loans.

Large loans often end up in more than one deal: the loan is split into pari passu notes and each note goes to a different trust. In BANK5 2025-5YR14, the $51 million Spiral note was one piece of a whole loan with $2.03 billion of other senior notes and $773 million of subordinate notes (prospectus, whole loan summary).

What makes a CMBS loan different for the borrower

• Non-recourse, with carve-outs. The property secures the loan; a guarantor is liable only for listed bad acts. See non-recourse CMBS loans.
• Fixed rate, fixed term, often interest-only. 86.9% of the BANK5 2025-5YR14 pool by balance was interest-only for the full term. See interest-only CMBS loans.
• Prepayment is engineered, not negotiated. A typical schedule reads like the Spiral loan’s L(27),D(26),O(7): 27 payments locked out, 26 payments in which the borrower may defease, then a 7-payment open period. Other loans use yield maintenance. See prepayment penalties.
• A servicer, not a relationship lender. Consents, assumptions and releases run through the servicer under the trust’s rules. See servicer consent and loan assumption.
• Tax rules limit change. Because the trust is a REMIC, the loan generally cannot be significantly modified unless it is in default or default is reasonably foreseeable, and no new money can be added to it. See loan modification.
• Cash management and reserves. Lockboxes and springing cash traps are standard, as are reserves.

In exchange, CMBS can offer higher leverage than many banks, long fixed-rate terms, non-recourse structure and a lender that does not care about deposit relationships. The trade-offs side by side: CMBS loan pros and cons and CMBS vs bank loans.

The rules that shape a deal

• SEC Regulation AB II (17 CFR 229.1100-1125), adopted in 2014 (79 FR 57184), sets disclosure for public deals, including Schedule AL loan-level data (Item 1125) filed on Form ABS-EE, a CEO certification, and an independent asset representations reviewer.
• Credit risk retention (17 CFR part 246) makes the sponsor, or a qualified B-piece buyer, keep 5% of the credit risk. See risk retention.
• REMIC tax rules (26 USC 860A-860G; 26 CFR 1.860G-2) let the trust pass income through untaxed, provided its pool stays fixed. See REMIC.
• The pooling and servicing agreement is the contract that applies all of this to one trust. See the PSA.

Why the data is public, and what you can do with it

Because public CMBS trusts must file Schedule AL data, every securitized loan’s rate, size, leverage, coverage, servicer and payment status is on EDGAR. This site builds on that file: CMBS loan rates by property type and term, CMBS statistics, the maturity wall, CMBS lenders ranked by recent loans, and the special servicers who hold troubled loans. If your loan is already in a trust, who is my special servicer finds it.

Where to go next

• Financing a property: what is a CMBS loan, how to get one, requirements, and CMBS underwriting.
• Living with one: defeasance, selling a property with a CMBS loan, when it is maturing.
• In trouble: special servicing, maturity default, loan modification.
• Every term on this page, defined: the CMBS glossary.

Sources: BANK5 2025-5YR14 prospectus (424B2) and pooling and servicing agreement (8-K Exhibit 4.1), both filed April 2, 2025: cover page, “Summary of Terms”, “Mortgage Pool Characteristics”, “Description of the Certificates”, “Pooling and Servicing Agreement: Advances” and Annex A-3. Regulations as cited, eCFR current text.