mbswal

Weighted average life of mortgage pool

Syntax

WAL = mbswal(Settle,Maturity,IssueDate,GrossRate)

WAL = mbswal(___CouponRate,Delay,PrepaySpeed,PrepayMatrix)

Description

WAL = mbswal(Settle,Maturity,IssueDate,GrossRate) computes the weighted average life, in number of years, of a mortgage pool, as measured from the settlement date.

WAL = mbswal(___CouponRate,Delay,PrepaySpeed,PrepayMatrix) specifies options using one or more optional arguments in addition to the input arguments in the previous syntax.

Examples

Determine the Weighted Average Life of a Mortgage Pool

This example shows how to determine the weighted average life of a mortgage pool, given a pass-through security with the following characteristics.

Settle = datetime(2002,4,15);
Maturity = datetime(2030,1,1);
IssueDate = datetime(2000,1,1);
GrossRate = 0.08125;
CouponRate = 0.075;
Delay = 14;
Speed = 100;

WAL = mbswal(Settle, Maturity, IssueDate, GrossRate, ... 
CouponRate, Delay, Speed)

WAL = 
10.5477

Input Arguments

Settle — Settlement date

datetime array | string array | date character vector

Settlement date, specified as an NMBS-by-1 vector using a datetime array, string array, or date character vectors. Settle must be earlier than Maturity.

To support existing code, mbswal also accepts serial date numbers as inputs, but they are not recommended.

Maturity — Maturity date

datetime array | string array | date character vector

Maturity date, specified as an NMBS-by-1 vector using a datetime array, string array, or date character vectors.

To support existing code, mbswal also accepts serial date numbers as inputs, but they are not recommended.

IssueDate — Issue date

datetime array | string array | date character vector

Issue date, specified as an NMBS-by-1 vector using a datetime array, string array, or date character vectors.

To support existing code, mbswal also accepts serial date numbers as inputs, but they are not recommended.

GrossRate — Gross coupon rate (including fees)

vector of decimal values

Gross coupon rate (including fees), specified as an NMBS-by-1 vector of decimal values.

Data Types: double

CouponRate — Net coupon rate

GrossRate (default) | vector of decimal values

(Optional) Net coupon rate, specified as an NMBS-by-1 vector of decimal values.

Data Types: double

Delay — Delay (in days) between payment from homeowner and receipt by bondholder

0 (no delay between payment and receipt) (default) | vector

(Optional) Delay (in days) between payment from homeowner and receipt by bondholder, specified as an NMBS-by-1 vector.

Data Types: double

PrepaySpeed — Speed relative to PSA standard

0 (no prepayment) (default) | vector

(Optional) Speed relative to PSA standard, specified as an NMBS-by-1 vector. The PSA standard is 100.

Note

Set the PrepaySpeed to [] if you input a customized PrepayMatrix.

Data Types: double

PrepayMatrix — Customized prepayment vector

matrix

(Optional) Customized prepayment vector, specified as a NaN-padded matrix of size max(TermRemaining)-by-NMBS. Each column corresponds to each mortgage-backed security, and each row corresponds to each month after settlement.

Note

Use PrepayMatrix only when PrepaySpeed is unspecified.

Data Types: double

Output Arguments

WAL — Weighted Average Life of MBS, in number of years

vector

Weighted Average Life (WAL) of MBS, in number of years, returned as a NMBS-by-1 vector.

More About

Weighted Average Life

The Weighted Average Life (WAL) of a mortgage pool is a measure used to estimate the average time until the cash flows from the pool of mortgages are received, weighted by the present value of those cash flows.

References

[1] PSA Uniform Practices, SF-49

Version History

Introduced before R2006a

R2022b: Serial date numbers not recommended

Although mbswal supports serial date numbers, datetime values are recommended instead. The datetime data type provides flexible date and time formats, storage out to nanosecond precision, and properties to account for time zones and daylight saving time.

To convert serial date numbers or text to datetime values, use the datetime function. For example:

t = datetime(738427.656845093,"ConvertFrom","datenum");
y = year(t)

y =

        2021

There are no plans to remove support for serial date number inputs.