Z-Tranche Accretion and Principal Payments in CMOs

Summary

The document raises questions about how a Z-tranche in a collateralized mortgage obligation handles coupon interest and principal. It describes the tranche as a mechanism intended to support scheduled amortization for more senior classes backed by the same mortgage pool. The questioner proposes that interest may be added to the Z-tranche’s notional in some periods, with no investor payment, or that the tranche may receive interest and principal as it amortizes.

It also asks whether accretion and amortization must occur in fixed phases, or could alternate across payment dates, and whether a portion of coupon interest could be paid while the remainder is added to notional. The document provides no answer, examples, or deal terms establishing which behaviors are permitted. These mechanics depend on the specific CMO structure and its governing documentation, so the questions alone do not establish a general rule for Z-tranche cash flows.

Key ideas

• A Z-tranche is described as supporting scheduled payments to more senior CMO classes.
• The document asks whether coupon interest can be added to tranche notional instead of being paid out.
• It questions whether accretion and amortization must follow fixed phases or can alternate over time.
• It asks whether coupon interest can be divided between cash payment and accretion.
• No answer or transaction terms are supplied, so the document does not establish the governing rules.

Tags

# Collateral Mortgage Obligation Z-Tranches


# Collateral Mortgage Obligation Z-Tranches












I would like to inquire about a specific type of Z-Tranches used in CMOs

As part of the different collateral mortgage obligation (CMO) structures, we see a specific type of tranches named "Z-Tranche". It is specifically designed to act as a cushion to be able to secure the promised amortization on the other more senior tranches that shares the same pool of loans. To fulfill that purpose, on each payment date, I understand that the Z-Tranche can:

- Either re-invest the interest coupon into the notional, and therefore no payment (interest or capital) is passed to the investor of this tranche. In that case, the published pool factor would be greater than that of the previous month

- Or amortize as a normal MBS does, by paying interest and capital based on the published pool factor that is lower than that of the previous month

Though normally a Z-Tranche starts by acrreting for a series of date and thereafter at a given moment starts amortizing back, there is no rule for that e.g. this tranche can acrrete on the first period, amortize on the second one and then again accrete on the third one

First, is my above understanding correct? Second, can this tranche have a partial accretion of coupon to the notional? (i.e. pay a small part and re-invest the rest into the notional)

Cheers,

Shown in full with attribution under the source's licence. Licence: CC BY-SA 4.0 (Stack Exchange)

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.