Rental Property or Index Fund? Run the Real Numbers First
2026-07-18 · 4 min read · Real Estate
Real estate looks like the obvious wealth play until you account for the down payment's opportunity cost, the vacancies, and the hours. Here is how to compare a rental honestly against a market portfolio, plus a free tool that does the after-tax math for you.
"Buy a rental, the tenant pays your mortgage, and you build wealth in your sleep." It is one of the most repeated ideas in personal finance, and it is not wrong. But it is rarely compared honestly against the simplest alternative: taking the same down payment and investing it in the market.
A rental can absolutely win. It can also quietly lose to an index fund while feeling like a success because the property value went up. The only way to know is to put both on the same after-tax footing.
What the rental pitch usually leaves out
A fair comparison has to count everything, not just the parts that flatter real estate.
• **The down payment has an opportunity cost.** That $100,000 down payment is $100,000 that is no longer in the market. Whatever the market would have done with it is the true hurdle the rental has to beat.
• **Cash flow is what is left after everything.** Not rent minus mortgage. Rent minus mortgage, taxes, insurance, maintenance, management, and a realistic vacancy allowance. The last three are the ones people leave out.
• **Appreciation is real but leveraged both ways.** Leverage magnifies gains and losses, and you still owe the bank on the down years.
• **Your time is a cost.** Tenants, repairs, and turnovers are hours. If you would not work those hours for free elsewhere, they belong in the math.
Where real estate genuinely pulls ahead
This is not an argument against rentals. Property has real structural advantages a brokerage account does not:
• **Depreciation** shelters a chunk of the cash flow from tax every year, even as the property appreciates.
• **Leverage** lets a modest down payment control a much larger asset.
• **A 1031 exchange** can defer the gain when you trade up, and the right ownership structure can carry real estate more tax-efficiently than most people realize.
Those advantages are exactly why you cannot eyeball this decision. The tax treatment is different enough on each side that intuition is a bad guide.
Put both on the same footing
Our free [**Rental vs. Invest** calculator](https://eiduktaxandwealth.com/rental-vs-invest) runs the honest comparison: the rental (cash flow, appreciation, and the tax benefits including depreciation) against the same money invested in a diversified portfolio, both after tax, over your holding period. You enter the purchase, the financing, your real operating assumptions, and your bracket. It shows you which path actually builds more wealth for your situation.
Sometimes the rental wins clearly, and you should buy it. Sometimes the index fund wins, and you just saved yourself years of being a landlord for a return you could have had passively. Either way, you decide on the numbers instead of the story.
Model your own deal with the [Rental vs. Invest tool](https://eiduktaxandwealth.com/rental-vs-invest), or [browse all of our free tools](https://eiduktaxandwealth.com/#tools).