What it means
A large commercial mortgage is often too big or too risky for one lender's book, so the loan is split into pieces with a strict pecking order. The A-note takes the senior claim on the property's income and sale proceeds, and the B-note stands behind it, paid only after the A-note receives its due.
Subordination is the entire point: if the borrower defaults and the building sells for less than the loan, the B-note absorbs the first loss, and in exchange for acting as the shock absorber its holder earns a meaningfully higher rate. The two notes are separate contracts over the same mortgage, governed by an agreement between their holders.
That intercreditor or co-lender agreement decides who controls decisions: typically the A-note leads while the loan performs, and control shifts to the B-note when defaults bite, because that is whose money is burning. For borrowers, the split brings larger loans and keener blended pricing at the cost of two masters, so consent rights, cure rights and transfer restrictions deserve as much attention as the rate sheet.
The structure scales up into securitisation. Whole loans split into A and B notes can feed commercial mortgage-backed securities, where the senior pieces earn investment-grade ratings and the junior pieces attract yield-seeking buyers, and the B-piece of a CMBS deal plays the same first-loss role at the bond level.
Some structures stack multiple junior notes, each with its own attachment point, turning one loan into a miniature capital structure. Regulators recognise the economics.
United States risk-retention rules for CMBS let a sponsor satisfy its obligation by selling the eligible horizontal residual interest, the first-loss slice, to a third-party purchaser who must hold it, so the B-buyer's skin in the game is deliberately engineered into the system. For investors, B-notes are a leveraged view on a single building.
Returns look like loan interest in good times and can fall to zero quickly in bad times because the cushion below the B-note is thin or absent, so valuation starts from the property, not the rate sheet: the buyer estimates the building's worth under stress, subtracts the senior claim, and asks whether the remainder covers the note with margin. That attachment-point arithmetic, not the coupon, decides the price.
Workout skills separate successful B-note investors from casualties. When default comes, the junior holder often takes control of the remedy process, negotiating with the borrower, funding protective advances and sometimes ending up owning the building, and B-note holders typically receive servicer reports and site-visit rights, so monitoring the tenancy and rent roll closely is the only early warning the cushion below provides.
Buyers without that capability are renting risk they cannot manage.
In practice
Real-world examples.
Example
A bank originates a $50 million mortgage and syndicates the junior $10 million as a B-note to a debt fund. The bank keeps the senior $40 million on its books and reduces its exposure to a single building. The debt fund accepts the higher yield in return for taking the first loss.
Example
A CMBS sponsor sells the deal's first-loss B-piece to a third-party purchaser to meet risk-retention rules. The purchaser must hold the piece rather than resell it quickly. Its decision to buy at a given price signals how it rates the underlying loans.
Example
A B-note holder exercises its cure right, paying the borrower's missed instalments to keep control of the workout. The payments protect its position ahead of a possible foreclosure. It then negotiates a restructuring with the borrower and the senior lender.
Formula
Calculation
Loss allocation follows subordination: a loss on the loan hits the B-note until it is exhausted, and only then the A-note. B-note loss = min(total loan loss, B-note principal); A-note loss = max(0, total loan loss - B-note principal).
Worked example. A $60,000,000 loan is split into a $40,000,000 A-note and a $20,000,000 B-note on a property valued at $80,000,000. The A-note covers the first 50% of value and the B-note covers the next 25%. If the property sells for $45,000,000, the shortfall is $60,000,000 - $45,000,000 = $15,000,000.
The B-note takes the whole $15,000,000 loss, which is 75% of its $20,000,000 principal, and the A-note takes none. If the sale had instead raised only $30,000,000, the shortfall would be $30,000,000: the B-note would lose all $20,000,000 and the A-note would lose the remaining $10,000,000, or 25% of its principal.Case study
Seen in the real world.
This is a fictional example. An investor buys the $12,000,000 B-note under a $48,000,000 A-note on an office tower at an 11% coupon, which pays $1,320,000 of interest a year. Two years later the building sells at a $10,000,000 loss against the combined $60,000,000 loan. The B-note absorbs the whole $10,000,000 loss, so it recovers only $2,000,000 of its principal, and the A-note emerges whole.
With two years of interest of $2,640,000, the investor's total return is $4,640,000 against $12,000,000 invested, a net loss of $7,360,000. The same investor had judged the building's stress value to be well above the senior claim, but a major tenant left sooner than expected. The lesson was that the B-note's cushion is thin, and that the rent roll deserved monthly attention from the day of purchase.
Watch out
Common mistakes.
- Pricing a B-note like a bond with a rating. The risk is a leveraged bet on one property's value above the attachment point, and ratings rarely apply.
- Ignoring the co-lender agreement. Control, cure, and buyout rights decide outcomes in default as much as the loan terms do.
- Assuming senior comfort extends downward. A conservative A-note loan-to-value says nothing about the B-note, whose cushion is only the equity below it.
Questions
People also ask.
What is the difference between an A-note and a B-note?
Both are slices of one mortgage; the A-note is paid first and the B-note takes losses first in exchange for a higher rate.
Who buys B-notes?
Opportunistic debt funds and investors comfortable with property-level risk and the workout process.
How do B-notes relate to CMBS?
Securitisations replicate the same senior-junior logic at bond level, with the B-piece as the first-loss class sold to third-party buyers.
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