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Strategic Financial Management · Securitization

Types of Securitized Instruments: ABS, MBS and PTC

Updated 11 October 2026 · Fact-checked

Securitized instruments are securities issued against a pool of receivables. ABS are backed by assets such as vehicle or credit card loans. MBS are backed by mortgages. In pass-through certificates, collections are passed on to investors pro rata. In pay-through, cash flows are restructured into tranches. To solve questions, identify the collateral, then the cash-flow rule.

Understand Types of Securitized Instruments (ABS, MBS, PTC)

Securitization converts illiquid receivables into tradable securities. An originator pools loans and sells them to a special purpose vehicle (SPV). The SPV issues securities to investors, and the pool's collections pay them. The type of instrument depends on what backs it and how cash flows are paid out.

Asset-backed securities (ABS) are backed by non-mortgage receivables, such as auto loans, personal loans, credit card receivables or equipment leases. Mortgage-backed securities (MBS) are backed by loans secured on real estate. MBS backed by residential mortgages are RMBS, and those backed by commercial property loans are CMBS. The key difference is collateral, not structure. MBS carry heavy prepayment risk, because borrowers can repay home loans early.

Pass-through certificates (PTC) give investors an undivided share in the pool. The SPV passes on interest and principal collected, less servicing fees, pro rata to all holders. The certificates are not debt of the SPV; investors hold a beneficial interest in the pool. Investors bear the pool's prepayment and default risk directly. Every holder is in the same position, so there is no tranching.

Pay-through securities are debt obligations of the issuer, backed by the pool. Collections are used to pay the debt, but the payments need not mirror collections. Cash flows can be reshuffled into tranches with different maturities and risk. The reshuffling gives investors a choice. It redistributes prepayment risk among the classes rather than removing it: earlier or senior classes get more predictable cash flows, while later or support classes absorb more uncertainty, including extension and reinvestment uncertainty. In a pay-through, the assets typically remain on the issuer's balance sheet and the securities are the issuer's own debt obligations.

Other instruments build on these. A CDO (collateralised debt obligation) pools bonds or loans and issues tranches ranked by seniority. STRIPS split a pool's cash flows into separate interest-only (IO) and principal-only (PO) securities. IO value falls when prepayments rise, because interest stops. PO value rises, because principal comes back sooner.

Key rules to remember

Pass-through payment to investors
Investor receipt = (Interest + Principal collected) − Servicing fee
Paid pro rata to certificate holders. Principal includes prepayments received.
Pro rata share
Holder's receipt = Holder's units ÷ Total units × Net collections
Use for every pass-through question. All units rank equally.
Tranche waterfall rule
Senior tranche is paid first; losses hit the equity/junior tranche first
Applies to pay-through, CDO and structured MBS. Principal is paid in order of seniority.
Prepayment effect on STRIPS
Higher prepayment → IO value falls, PO value rises
IO depends on outstanding principal. Prepayment shrinks that principal, so the interest stream ends early and IO falls in value. Prepayment also hurts holders who bought at a premium over par, because they lose the above-par coupon stream early. PO gains from early receipt of the fixed principal.

How to solve Types of Securitized Instruments (ABS, MBS, PTC) questions

Use this method for both theory and numerical questions on securitized instruments.

  1. 1Identify the collateral: mortgages mean MBS, other receivables mean ABS.
  2. 2Identify the structure: undivided pro rata share means pass-through; restructured, tranched debt means pay-through.
  3. 3List the pool's collections for the period, split into interest and principal, and include prepayments.
  4. 4Deduct servicing or trustee fees to get net distributable cash.
  5. 5Apply the payout rule: pro rata for PTC, or the seniority waterfall for tranches.
  6. 6Check the risk each investor bears: prepayment, default, reinvestment.
  7. 7State the conclusion in one line, such as which instrument suits which investor, or the amount received.

Quickest way: Collateral, structure, payout

When to use it: Use for MCQs and for short comparison questions where you must classify an instrument in under a minute.

  1. Read the collateral word: mortgage or housing means MBS; vehicle, card, or other loans mean ABS.
  2. Read the payout word: pro rata or undivided share means PTC; tranches or classes means pay-through or CDO.
  3. For IO or PO, ask what prepayment does: it hurts IO and helps PO.
  4. For numbers, deduct fees first, then split pro rata or in seniority order.

Common mistakes in Types of Securitized Instruments (ABS, MBS, PTC)

  • Treating ABS and MBS as different structures.

    The names sound like separate mechanisms.

    Fix: Remember that the difference is the collateral. Both can be pass-through or pay-through.

  • Saying pass-through certificates are tranched.

    Mixing them up with pay-through securities.

    Fix: PTC holders share pro rata. Tranching belongs to pay-through, CDOs and structured deals.

  • Forgetting to deduct servicing fees before distributing.

    Students distribute gross collections.

    Fix: Always compute net collections first, then distribute.

  • Saying prepayment helps all investors.

    Early cash looks good.

    Fix: Prepayment hurts IO strips and investors who bought at a premium over par, because they lose the above-par coupon stream early. That is why IO falls in value. It helps PO strips, which get principal sooner. It also creates reinvestment risk.

  • Treating a pass-through as the originator's debt.

    Confusion with pay-through, which is debt of the issuer.

    Fix: In a PTC, investors own a share of the pool. A pay-through is a debt obligation backed by the pool.

Worked examples

Example 1

An SPV holds a pool of auto loans and has issued 1,000 pass-through certificates. In a month it collects interest of ₹6,00,000 and principal of ₹14,00,000 (including prepayments). Servicing fee is ₹1,00,000. Find the net amount paid to a holder of 50 certificates.

Show the solution
  1. Total collections = ₹6,00,000 + ₹14,00,000 = ₹20,00,000.
  2. Net distributable = ₹20,00,000 − ₹1,00,000 = ₹19,00,000.
  3. Holder's share = 50 ÷ 1,000 = 5%.
  4. Receipt = 5% × ₹19,00,000 = ₹95,000.

Answer: The holder receives ₹95,000. The pool is an ABS because it is backed by auto loans, and the pro rata payout shows it is a pass-through.

Example 2

A senior-subordinate (tranched) issue has Class A (₹60 crore, senior) and Class B (₹40 crore, subordinate) backed by a pool of ₹100 crore. Defaults lose ₹30 crore of the pool, so ₹70 crore of principal is recovered. Ignore interest for simplicity and apply the loss waterfall to principal only. Find how much principal each class recovers, assuming principal is paid to A first.

Show the solution
  1. Total principal recovered = ₹100 crore − ₹30 crore = ₹70 crore.
  2. Class A is paid first: it is owed ₹60 crore and the pool has ₹70 crore, so A receives ₹60 crore in full.
  3. Remaining = ₹70 crore − ₹60 crore = ₹10 crore.
  4. Class B is owed ₹40 crore and receives ₹10 crore.
  5. Loss to B = ₹40 crore − ₹10 crore = ₹30 crore.

Answer: Class A recovers ₹60 crore of principal; Class B recovers ₹10 crore and bears the entire ₹30 crore loss. The subordination of Class B protects Class A. This is a credit-enhancement feature of senior-subordinate structures. In a plain pass-through, there is no such protection, because the loss is shared pro rata by all holders.

Exam tips

  • For comparison questions, use two columns in your answer: collateral, cash-flow rule, risk, and investor type.
  • In MCQs on IO and PO strips, think prepayment direction first.
  • If a numerical gives fees, deduct them before any split.
  • Write a closing line saying which investor bears which risk. It earns marks in application answers.

Practice questions from Securitization

Types of Securitized Instruments (ABS, MBS, PTC) in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Types of Securitized Instruments (ABS, MBS, PTC): frequently asked questions

What is the difference between pass-through and pay-through certificates?

In a pass-through, investors own an undivided share of the pool and receive collections pro rata. In a pay-through, the issuer issues debt backed by the pool and can restructure the payments into tranches. Pay-through gives more control over maturity and risk.

What is the difference between MBS and ABS?

MBS are backed by loans secured on real estate. ABS are backed by other receivables such as vehicle loans, credit card dues or equipment leases. Both can use pass-through or pay-through structures.

What are CDOs?

A CDO pools debt instruments such as bonds or loans and issues tranches ranked by seniority. Senior tranches are paid first and junior tranches absorb losses first.

What are STRIPS in securitization?

STRIPS separate a pool's cash flows into interest-only and principal-only securities. Prepayments reduce the value of the IO and raise the value of the PO.