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Mortgage Mathematics: Are Banks “Ripping Off” The Customer?
John Spencer Walker, Ju Zhou, Jon K. Kramer

Last modified: 2020-06-30

Abstract


In this pedagogical research, we answer two questions raised during our teaching of mortgage mathematics. The first question is: If someone takes out a fixed-rate mortgage and pays it off after only a few years, isn’t the bank “ripping off” the customer? The second question is: When is the interest portion of a monthly mortgage payment exactly equal to the principal portion? The first question is easier to answer because a mortgage is a financial contract with a known interest rate that the consumer agrees to pay. To provide a fixed payment, the mortgage mathematics dictates that a greater percentage of interest is paid in the early years. To answer the second question requires increasing the number of payments “N” to infinity to find the exact crossover point because the normally-discrete modeling of mortgage payments has no single payment where there’s a perfect 50/50 split between the interest and principal payments.


Keywords


mortgage analytics, fixed-rate mortgage