How to model a home loan

The planner offers plenty of flexibility and can handle many complicated real-world scenarios, but sometimes it can be tough to figure out how to do it. Check out this forum for discussion of how to model things like selling a house, long-term care expenses, and much more.
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Joined: Thu May 09, 2019 9:16 am

How to model a home loan

Post by i_heart_frp » Thu May 09, 2019 9:56 am

I'm in the process of buying a house and I'm trying to determine how to structure the home loan. I have been trying to use FRP to model the long term impacts of different scenarios. The problem I'm having is that the outcomes tend to be the opposite of what I would expect.

Consider two 30-year loan scenarios: 15% down at 4.5% vs 20% down at 4.375%. I would expect that putting less down at a slightly higher interest rate would yield the larger average Median Ending Portfolio Value and Probability of Success but it's always the opposite.

Here's how I've attempted to model the loan: I've separated out the principal and interest (PI) from the taxes, insurance, and maintenance (TIM). I've modeled the PI as a No-COLA expense for 30 years, and the TIM to track inflation to End of Plan (hopefully this is a forever home). I've also added an expense entry for the sum of Down Payment, Settlement Costs, Prepaids for Start of Plan.

I have my investing style set to Above Average Risk. I would assume that the average returns of the market (9.5%) would more than make up for the differences in interest rates but that's not what I'm seeing.

Is there something I'm missing in my modeling that could account for this behavior?

Posts: 514
Joined: Thu Feb 28, 2008 6:48 pm

Re: How to model a home loan

Post by jimr » Thu May 09, 2019 5:22 pm

First, it's essential to look at the year-by-year detailed view tab after running the planner to verify that the simulation is handling all the cash flows the way you expect. In the details view tab, you can click the "show more detail" radio button on the top right to see extra information and also if you right-click on a column header in the detailed view table, there's a popup menu that has an option to "show all columns" which displays even more information. This can be helpful in trying to understand what might be happening when the results aren't what you expect.

Aside from that, It's tough to say what might be happening without seeing the details. If you wouldn't mind depersonalizing your data file and changing around all the numbers to obscure all personal information, I'd be happy to take a look to see what's going on.

You can email the scrubbed .frp file to

Again though, since email is not secure, please be sure to change around the numbers so the file doesn't contain any of your actual financial information.


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