Independent solution

How to solve this Mortgage with Extra Payments question

Setup

Setup

Compute the original 360-month mortgage payment at 0.5% per month. Treat the extra payments as a separate cash-flow stream and find their time-0 present value.

R=200000/a3600.005=1199.10R=200000/a_{\overline{360}|\,0.005}=1199.10

Model

Model

Subtracting that value from the original principal leaves 158,070.46 to be amortized by the regular payment. Solving the annuity equation gives 215.78 regular-payment months.

PV0(extra payments)=41929.54PV_0(\text{extra payments})=41929.54

Compute

Compute

The payoff therefore occurs on the next scheduled payment date corresponding to December 31, 2020.

158070.46=1199.10an0.005n=215.78158070.46=1199.10a_{\overline n|\,0.005}\Longrightarrow n=215.78

Answer

Answer

The calculation gives December 31, 2020 for mortgage with extra payments, matching published choice C.

December 31, 2020(C)\boxed{\text{December 31, 2020}\quad\text{(C)}}