CMBS tranches: how one pool of loans becomes 16 classes of bonds
By Brad Beattie, Director, Capital Markets, Janover Capital LLC · Published
A CMBS tranche is one class of the bonds a trust issues against its pool of loans. Classes are stacked by seniority: the top classes get interest and principal first and take losses last; the bottom, first-loss classes take losses first. In BANK5 2025-5YR14, the senior classes had 30% credit support, meaning 30% of the pool sat beneath them.
Every figure below is from the BANK5 2025-5YR14 prospectus (424B2, filed April 2, 2025), “Summary of Certificates” and “Description of the Certificates”. The pool: 25 loans on 72 properties, $884,437,753.
The capital stack of a real conduit deal
| Class | Balance | Share of pool | Size | Credit support | Coupon type |
|---|---|---|---|---|---|
| A-1 | $5,730,000 | 0.648% | 30.000% | Fixed 4.822% | |
| A-2 | $120,500,000 | 13.624% | 30.000% | Fixed 5.165% | |
| A-3 | $492,876,000 | 55.728% | 30.000% | Fixed 5.646% | |
| A-S | $88,444,000 | 10.000% | 20.000% | WAC cap 6.072% | |
| B | $44,222,000 | 5.000% | 15.000% | WAC cap 6.474% | |
| C | $33,166,000 | 3.750% | 11.250% | WAC cap 6.463% | |
| D | $9,950,000 | 1.125% | 10.125% | Fixed 4.250% | |
| E | $13,488,000 | 1.525% | 8.600% | Fixed 4.250% | |
| F-RR | $14,151,000 | 1.600% | 7.000% | WAC 6.529% | |
| G-RR | $11,055,000 | 1.250% | 5.750% | WAC 6.529% | |
| J-RR | $12,161,000 | 1.375% | 4.375% | WAC 6.529% | |
| K-RR | $38,694,752 | 4.375% | 0.000% | WAC 6.529% |
Two things jump out. Seven-tenths of the deal is one block of senior bonds (A-1 through A-3 together are 70.0% of the pool). And the bottom class is far larger than the slices just above it: K-RR alone is 4.375% of the pool, a thick first-loss layer that must be worn through before anything else is touched.
Credit support, in plain terms
A class’s credit support is the percentage of the pool subordinate to it. Read down the column: 30% under the senior A classes, 20% under A-S, 15% under B, and so on to 0% under K-RR. The step from one class to the next equals the size of the class in between: A-S is 10% of the pool, so support drops from 30% to 20% across it.
A worked example. Suppose one $40 million loan in this pool is liquidated and recovers half its balance. The $20 million realized loss is allocated to the bottom class first, so Class K-RR’s balance falls from $38,694,752 to $18,694,752, and every class above it is untouched. Only after K-RR is written to zero would J-RR take a loss, then G-RR, F-RR, E, D, C, B and A-S, and finally the senior A classes pro rata (prospectus, “Subordination; Allocation of Realized Losses”).
Credit support comes from subordination alone in a conduit deal. The prospectus cover says so directly: credit enhancement “will be provided solely by certain classes of subordinate certificates.” There is no bond insurance, no overcollateralization and no guarantee; compare CMBS vs ABS.
The waterfall: who gets paid first
Each month the certificate administrator applies the cash available in this order (prospectus, “Priority of Distributions”):
- Interest to the senior A classes and the X classes, pro rata.
- Principal to the senior A classes in sequence: A-1 until it is paid off, then A-2, then A-3. If the subordinate classes have all been wiped out by losses (the “Cross-Over Date”), the A classes share principal pro rata instead.
- Reimbursement of any losses previously allocated to the senior classes.
- Then the same three steps for A-S, then B, then C, then D, E, F-RR, G-RR, J-RR and K-RR, each in turn.
That sequencing is why the classes have different lives. With most of this pool interest-only, little principal arrives before the loans mature, so Class A-1 has an expected weighted average life of 2.43 years and a principal window of May 2025 to November 2029, while the classes from A-S down are all expected to be paid in a single month, April 2030, at about 4.98 years. Yield maintenance charges and prepayment premiums are distributed separately and do not follow the main waterfall.
Coupon types: fixed, WAC cap, WAC
- Fixed: a set pass-through rate (Classes A-1, A-2, A-3, D, E here).
- WAC cap: the lesser of a fixed rate and the pool’s weighted average net mortgage rate (A-S, B, C).
- WAC: the pool’s weighted average net mortgage rate itself (the RR classes).
- Interest-only (X classes): the excess of the pool’s weighted average net rate over the rates on the classes they reference. Class X-A’s rate is the weighted average net mortgage rate minus the weighted average rate on Classes A-1, A-2 and A-3; its notional amount shrinks as those classes are paid down.
Control: the tranche that runs your loan
The stack also decides who controls servicing. In BANK5 2025-5YR14 the controlling class is the most junior of the RR classes whose balance, after any appraisal reductions are applied, is still at least 25% of its original balance; at closing that was Class K-RR. Its holder, through the directing certificateholder, can consent to or object to major decisions on loans and can replace the special servicer. When Class F-RR falls below 25% of its original balance (counting appraisal reductions), a Control Termination Event occurs and consent rights give way to consultation; those end too once no RR class keeps 25% of its original balance, a Consultation Termination Event. Appraisal reductions are why a troubled loan can shift control: see appraisal reduction and the B-piece.
Why this matters if you borrow
Your loan does not sit in a tranche; the whole pool backs every class. But the stack explains the behavior you meet:
- Senior bondholders want certainty, which is why CMBS loans are standardized and hard to change. See CMBS loan terms.
- The first-loss investor reviewed your loan before the deal closed, chose the special servicer and must sign off on major decisions. See special servicing and loan modification.
- Interest-only collateral leaves little principal paid before maturity, which is why refinancing risk concentrates at the maturity wall.
Related: CMBS primer, risk retention, how CMBS bonds are rated, and the glossary.
Sources: BANK5 2025-5YR14 prospectus, cover page, “Summary of Certificates” and footnotes, “Certificate Balances and Notional Amounts”, “Description of the Certificates” (Distributions, Priority of Distributions, Subordination; Allocation of Realized Losses), “Pooling and Servicing Agreement” (The Directing Certificateholder; Control Termination Event). Percentages of the pool for Classes D through K-RR computed from the class balances and the initial pool balance.
Questions people ask
What is a tranche in CMBS?
A tranche (or class) is one slice of the bonds a CMBS trust issues. Each class has its own balance, interest rate and place in the payment order. Senior classes are paid first and lose money last; junior classes are paid later, earn more, and absorb losses first.
What does credit support mean?
Credit support is the share of the pool that sits below a class. The senior classes of BANK5 2025-5YR14 had 30% credit support: losses on the loans would have to exceed 30% of the pool balance before those classes lost principal.
What are the X classes?
Interest-only strips. They have no principal, only a notional balance tied to other classes, and they collect the excess of the loans' interest over what those classes pay. In BANK5 2025-5YR14, Class X-A's notional amount equals the combined balance of Classes A-1, A-2 and A-3.
What does the RR in Class F-RR mean?
Risk retention. Classes F-RR, G-RR, J-RR and K-RR together form the eligible horizontal residual interest that the B-piece buyer holds to satisfy the federal risk retention rule.
Does my loan's tranche matter to me as a borrower?
Your loan is not in a tranche; the whole pool backs every class. What matters is who holds the bottom classes, because that investor usually appoints the special servicer and must consent to major decisions on your loan.
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