practical investment management by robert.a.strong slides ch20

CHAPTER TWENTY

Practical Investment Management

Robert A. Strong

MORTGAGE-BACKED SECURITIES

South-Western / Thomson Learning © 2004 20 - 2

Outline

Mortgages Types Mortgage Mathematics Mortgage Risk

The Mortgage Backed Securities Market History Types of Securities


Outline

Considerations in Pricing MortgageBacked Securities The Importance of Prepayment Rates The PSA Convention The Risks of MBS The Risk of Collateralized Mortgage Obligations The Risk of Stripped Mortgage Backed Securities


Introduction

A mortgage is a loan with real estate as collateral. The lender, called the mortgage originator, often charges points as a fee for preparing and placing the mortgage.

It is quite common for the lender to sell the mortgage to another party.

The homeowner may be unaware of this, as the lender normally continues to be the mortgage servicer.


Mortgages: Types

A fixed rate mortgage is one with payments based on a set interest rate that does not change.

An adjustable rate mortgage (ARM), also called a variable rate mortgage, has an interest rate that moves with some market interest rate, such as the Treasury bill rate.

Most ARMS have an annual reset to the interest rate. Many also have either a cap or a floor on the interest rate.


Mortgages: Types

With a convertible mortgage, the borrower has the option to exchange it for a fixed rate at the prevailing ARM rate.

There are other mortgage arrangements: biweekly - payments are due every two weekssemi-monthly - payments are due two times

each monthgraduated payment - the monthly payments

increase following a predetermined schedule


Mortgages: Types

shared appreciation - the borrower splits the rise in the value of the property with the lender in exchange for a reduced interest rate

reverse - the homeowner sells the property to a bank and receives monthly mortgage payments


Mortgage Mathematics

There will be 30×12 = 360 monthly payments at a monthly interest rate of 8÷12 = 0.66667%

Example :

A bank approves a prospective homeowner for a 30-year, $100,000 mortgage at an 8% annual rate.



So:

36066667.0166667.0

1

66667.0

1000,100$ C

The monthly payment will be $733.76

For an annuity:

NRRR

C1

11value present

C = the monthly paymentR = the monthly interest rateN = the number of payments

where



If the borrower pays the bank $1,500 instead of $733.76 for the thirteenth payment, how will the amortization schedule be affected?

The bank considers the extra $766.24 the borrower paid a principal reduction, and the anticipated life of the loan will decrease.


Mortgage Risk

Default risk is the risk that the borrower is unable or unwilling to repay the debt as agreed.

Interest rate risk is the risk that the general level of interest rates rises, such that the value of the mortgage’s cash flow stream declines.

Prepayment risk is the risk of an early payment of the original mortgage, such as when the home is sold or when the mortgage is refinanced at a lower rate.


The Mortgage Backed Securities Market

The Federal National Mortgage Association (Fannie Mae), the Government National Mortgage Association (Ginnie Mae), & the Federal Home Loan Mortgage Corporation (Freddie Mac) support the US mortgage market by providing liquidity, buying conforming mortgages from banks across the country for resale elsewhere.

The term mortgage-backed securities refers to all products based on mortgage loans.


Types of Securities

A pass-through security is a share of a poolof mortgages.

The holders receive a monthly check for theirportion of the scheduled principal and interest payments, plus their share of any prepayments that may occur.

Individual Individual Individual Mortgages Mortgages Mortgages

Mortgage Pool

Pass Through Security


Pass-through securities may be issued and guaranteed by a government agency, or they may be private label.

Two types of derivative securities that spring from pass-through securities are collateralized mortgage obligations and stripped mortgage-backed securities.

Types of Securities


Types of Securities

A collateralized mortgage obligation (CMO) isa security backed by a pool of mortgages and structured to transfer prepayment or interest rate risk from one group of security holders to another.

A given pool of mortgages backs two or moreclasses of securities called tranches.


Types of Securities


Mortgage Pool

A Tranche B Tranche C Tranche Other Tranches

Collateralized Mortgage Obligation


Types of Securities

Insert Table 20-3 here.


Types of Securities

With a sequential pay CMO, all the tranche holders receive monthly interest payments based on the principal amount outstanding in their tranche.

All principal payments go to the A tranche until the A tranche principal is completely returned. Only then will the investors in the next tranche begin to receive principal.


Types of Securities



Types of Securities

There are two types of stripped mortgage backed securities, or strips.

All the interest goes to the interest only (IO)security holders, while the entire principal goes to the principal only (PO) holders.


Mortgage Pool

Interest Only Security Principal Only Security


Considerations in Pricing Mortgage Backed Securities

The price risk of a MBS comes from the uncertainty about the timing of cash flows.

Prepayments can affect the realized return on a M BS substantially.

The offering memorandum for a M BS will state the assumptions used in estimating cash flows from the mortgage pool.

A benchmark assumption for the rate of mortgage prepayment is offered by the Public Securities Association (PSA).


Constant Prepayment Rate

The standard PSA assumption is that a 30-year mortgage will see prepayments of 0.2% for the first month and that prepayments will increase by 0.2% for each of the next 29 months, after which they remain constant.

The 0.2% per month prepayment assumption is called 100% PSA.




A MBS has default, interest rate, and prepayment risks.

Riskiness of Cash Flows

variable ratenon-callable

bond

fixed ratenon-callable

bond

principal onlysecurity

interestonly

security

$ AmountUnknown

TimingKnown

$ AmountKnown

TimingUnknown


Declining interest rates will increase thevalue of a cash flow stream and will lead to prepayments.

If a mortgage pool sells at a discount,prepayments will increase the value of each of the tranches, with the higher duration tranches benefiting the most.

If the pool sells at a premium, thenprepayments will reduce everyone’s yield, with the effect most pronounced for the holders of the longer duration tranches.

The Risk of Collateralized Mortgage Obligations


The Risk of Stripped Mortgage Backed Securities

Prepayment has different consequences forIO and PO strips. An extension of the mortgage decreases the value of the principal payments but increases the value of the interest payments.

Declining interest rates will increase thevalue of a series of known cash flows, as well as the likelihood of prepayment. Normally, the prepayment effect overwhelms the interest rate effect.


Review

Mortgages Types Mortgage Mathematics Mortgage Risk

The Mortgage Backed Securities Market History Types of Securities


Review

Considerations in Pricing MortgageBacked Securities The Importance of Prepayment Rates The PSA Convention The Risks of MBS The Risk of Collateralized Mortgage Obligations The Risk of Stripped Mortgage Backed Securities

practical investment management by robert.a.strong slides ch20

Documents

pricing mortgage

mortgage mathematicsfor

mortgage mathematicsexample

mortgage mathematicsif

convertible mortgage

mortgage servicer

mortgage originator

original mortgage