What does a house with an ADU or a duplex build in ten years?
Three things build it: your tenant covers part of every payment, the loan shrinks, and the price does whatever it does. Only the loan is arithmetic. On our example, a sale in year ten leaves $51,480 if the price never moved, and more if it rose.
WHAT MOST PEOPLE ARE NEVER TOLD
We call this get rich slow. The slow part is certain. The rich part is not, because it rests on a price nobody can predict. So we show the ten years at a flat price first.
The example is a $480,000 duplex in Texas, bought with an FHA loan and $28,800 in cash. Over ten years:
- The rent covers $165,330 of the payments, after set-asides, if it never changes.
- The loan falls by $81,186 on schedule, if you make every payment.
- A sale in year ten, after selling costs and paying off the loan, leaves $51,480 at a flat price, $148,188 at 2 percent a year and $282,658 at 4.3 percent. Your $28,800 is inside those figures.
The 4.3 percent is the national long-run average on the FHFA House Price Index since 1991. That index tracks houses, and one home over one decade can do far worse. What could wreck the plan:
- An empty side. That month costs the whole $3,945.
- A tenant who stops paying. The payment is still due.
- A large repair, in a month you did not pick.
- Tax and insurance rising. Unlike the loan payment, they are not fixed.
- A price that falls. Then a sale can leave less than you put in, or nothing.
- Selling early. Before year five, a flat-price sale costs you money.
GOOD TO KNOW
None of these figures is a promise. They need you to make every payment and hold through the bad months. If one empty month at the full $3,945 would put you behind, build savings before you buy.
Yours is a little different. They all are.
Tell us what you are looking at and what you are trying to do. We answer with the numbers on your situation.
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WHERE THIS COMES FROM
- Series Homes worked example: the assumptions are printed on the ten-year page. Selling costs of 8 percent of the price are a rule of thumb, not a quote.
- Federal Housing Finance Agency, FHFA House Price Index (purchase-only, national, January 1991 to August 2026): the source of the 4.3 percent a year. It measures single-family houses.
Researched and written by Series Homes. Checked against its sources on . Lending rules change. This page is general information, not a loan offer or legal or tax advice.