# How to calculate the monthly cash flows of Mortgage Pass through Security?

Suppose there is a $400 million mortgage pass-through security with a 7.5% pass-through rate, a weighted average coupon of 8.125% and a weighted average maturity of 357 months, how to compute the cash flows for the next two months assuming a 100 Principal Securities Association(PSA)? • Is this homework or self study? – kurtosis Sep 4 '20 at 15:33 • @kurtosis I am trying to study from the Fabozzi text book. Since this is a US based concept, I am not quite sure as to whether I should use the Single monthly mortality rate or the conditional prepayment rate? Could you provides some leads as to how to approach it? – Chandramouli Raman Sep 4 '20 at 17:20 • I know Chapter 23 of A Quantitative Primer on Investments with$R\$ has code for a CMO, so you could modify that to have everything in one tranche. – kurtosis Sep 4 '20 at 21:14