e. The quarterly prepayments of $5 million will be credited entirely to tranche A until tranche A is completely
retired. Then prepayments will be paid entirely to tranche B. The amortization schedule for tranche A for the first
year is shown below. This amortization schedule assumes that the trustee has a quarterly payment amount from the
mortgage pool of $1,613,350.
Interest Principal Remaining
However, since some of the mortgages will be paid off early, the actual payment received by the trustee from the
mortgage pool will decrease each quarter. Thus, the payment for the second quarter will decrease from $1,613,350 to
$1,532,385 (n = 119 quarters, i = 5 percent, mortgage principal = $94,636,500). The CMO amortization schedule for
tranche A given that the mortgage payments decrease with the prepayments is given below. The revised mortgage
payment for each quarter is shown in the last column.
Interest Principal Remaining Mortgage
f. The amortization schedules for tranches A and B are shown below. Again the mortgage payments from the
mortgage holders are assumed to decrease as the prepayments occur.
Amortization schedule for tranche A:
Tranche Interest Principal Remaining Mortgage
Amortization schedule for tranche B:
Tranche Interest Principal Remaining Mortgage
8. a. There are 180 monthly payments (15 years x 12 months). The GNMA monthly coupon rate is 8.5% – 0.5% = 8
b. Assume that the GNMA is only half amortized. There is a lump sum payment at the maturity of the GNMA that
equals 50 percent of the mortgage pool’s face value.