What it means
The process starts with an originator, typically a bank or a specialist lender, that has made a large number of similar loans. It sells that pool to a special purpose vehicle, a standalone entity created only to hold the loans, which then issues bonds backed by the borrowers' repayments.
Selling the loans achieves two things at once. The originator gets cash back to lend again instead of waiting years for the loans to run off, and the loans move off its balance sheet so the same capital can support more lending.
Investors are not sold a single undifferentiated claim. The cash flow is divided into tranches, with the senior tranche paid first and carrying the lowest yield, a mezzanine tranche paid next, and an equity or first-loss tranche that absorbs early defaults in exchange for the highest potential return.
That priority ordering is the whole design. Losses eat the equity tranche before touching mezzanine and only reach the senior tranche after everything below it is wiped out, which is how a pool of unremarkable consumer loans can support a highly rated bond at the top of the structure.
The risks are concentration, prepayment and opacity. If the underlying borrowers are all exposed to the same regional economy or the same lending standards, the diversification is more apparent than real, and investors who cannot see loan-level data are relying entirely on the originator's underwriting and the rating agency's model.
In practice
Real-world examples
Example 1
A car finance company sells $500m of loans into a securitisation, receives the proceeds within weeks, and writes new business with the same capital instead of waiting four years for the original loans to repay.
Example 2
A pension fund buys the senior tranche of an equipment lease securitisation at 5% because the tranche is rated highly, sits behind 20% of subordinated protection, and matches a known liability seven years out.
Example 3
A credit hedge fund buys the first-loss tranche of a consumer loan deal at a deep discount, having modelled the pool's default behaviour itself and concluded the market is pricing in losses roughly twice what the loan data supports.
Think of it
Think of a music streaming service. Instead of waiting for individual listeners to buy single tracks, artists pool thousands of streams together into an album, selling shares of the total royalty earnings to fans.
Formula
Calculation
Tranche interest = Tranche size x Tranche coupon
Residual to equity = Pool interest income - Senior interest - Mezzanine interest - Servicing and fees - Credit losses
Take a $500m pool of car loans yielding 8% a year, producing interest income of 8% x $500m = $40m. The structure issues a senior tranche of 80%, or $400m, at 5%; a mezzanine tranche of 12%, or $60m, at 7%; and an equity tranche of 8%, or $40m, that takes what is left. Senior interest is $400m x 5% = $20m and mezzanine interest is $60m x 7% = $4.2m. Servicing and administration fees run at 1% of the pool, or $5m. The residual to the equity tranche is $40m - $20m - $4.2m - $5m = $10.8m, a return of $10.8m / $40m = 27% on the equity slice, before any credit losses. If defaults cost the pool $6m in a bad year, the equity return falls to ($10.8m - $6m) / $40m = 12%, while the senior and mezzanine holders are paid in full.Case study
Seen in the real world
Northgate Auto Credit is a fictional lender created for this illustrative case study. It had originated $500m of car loans over three years and had run out of capacity, because every dollar lent was tied up until borrowers finished repaying, and its own credit line was fully drawn.
It sold the pool to a special purpose vehicle that issued $400m of senior notes at 5%, $60m of mezzanine notes at 7% and retained the $40m equity tranche itself. With pool income of $40m, senior and mezzanine coupons of $24.2m and $5m of servicing costs, the retained equity earned $10.8m in a normal year, and the $460m raised went straight back out as new loans.
Retaining the equity tranche was the point, not an afterthought. In this illustrative example it kept the lender's incentives aligned with investors, because sloppy underwriting would hit its own slice first, and when a mild recession pushed pool losses to $6m the senior investors were paid in full while Northgate absorbed the shortfall.
Watch out
Common mistakes
- Assuming a top rating means the deal is safe. A senior tranche can be highly rated while the underlying loans are mediocre, because the rating reflects the protection below it, not the pool's average quality.
- Ignoring prepayment risk. Borrowers repaying early shorten the life of the security and return capital when reinvestment rates may be worse.
- Treating pool diversification as automatic. Thousands of loans written to the same standards in the same region can behave like one large exposure in a downturn.
Questions
People also ask
What is the difference between an asset-backed security and a mortgage-backed security?
Both use the same structure, but a mortgage-backed security is backed specifically by property loans while asset-backed deals cover car loans, cards, leases and similar receivables.
Why does the originator often keep the equity tranche?
Retaining first-loss exposure signals confidence in the underwriting and is required by risk-retention rules in many markets.
Who actually collects the payments?
A servicer, often the original lender, continues to bill borrowers and pass the cash to the special purpose vehicle for a fee.