We use a contingent claims framework for valuing the the default and prepayment embedded options in certain British fixed-rate endowment mortgages, with a (capped) mortgage indemnity guarantee (MIG). This methodology provides a template for the borrower, lender, and insurer to compare mortgage terms, including the fairness of contract rates, arrangement fees, prepayment penalties, any MIG premiums required, and co-insurance exposure. With empirical inputs, this model may eventually be useful as a “mark-to-value” proxy for all parties, as expected parameters change (especially interest rate and house price levels, and expected future volatilities), for purposes of determining “valued added accounting”, appropriate reserves, and indeed for setting premiums and business drivers. Fixed-rate endowment mortgages differ from fixed-rate repayment mortgages primarily because, in the event of early termination, the amount owed by the borrower is a function of the evolution of the term structure of interest rates, whereas for a repayment mortgage it is pre-determined. We compare endownment and repayment mortgages for different levels of loan-to-value ratios, interest rate and house price volatilities.
Azevedo-Pereira, J. A., Newton, D., & Paxson, D. A. (2003). Fixed Rate Endowment Mortgage and Mortgage Indemnity Valuation. Journal of Real Estate Finance and Economics, 26(2-3), 197- 221. https://doi.org/10.1023/A:1022930825566