The question most rental calculators refuse to ask
Nearly every rental calculator tells you what a property returns. Almost none tell you whether that return is good — because "good" only exists relative to what else your money could be doing. A rental producing 6% a year sounds fine until you notice the same capital might have earned 8% elsewhere with no tenants, no roof, and no 3am phone calls. That gap is the opportunity cost of your down payment, and it's the whole subject of this calculator.
Why property often wins anyway: leverage. Put 25% down and your appreciation compounds on the full property value, not just the slice you paid for. Three percent appreciation on the whole asset is roughly twelve percent on your down payment before costs. Add mortgage paydown — tenants quietly converting your debt into equity every month — and property can beat an unlevered alternative even on unimpressive yields. Leverage is the structural edge. It is also, honestly, the structural risk: it magnifies losses with exactly the same efficiency.
Why the hold period decides the argument. Real estate charges you several percent to buy and several more to sell; an index fund charges almost nothing. Those costs savage short holds. But over a long one, leverage, paydown, and rent growth compound in property's favour while the one-time friction amortises into irrelevance. The answer commonly flips somewhere in the middle — so test several horizons instead of trusting one.
How this stays fair. Both paths compound at the same alternative rate: the property reinvests its positive cash flow there, and the alternative receives every dollar you'd otherwise have spent covering the property's shortfalls. Without that symmetry the comparison quietly flatters one side — the usual sin in property-versus-market arguments. Two honest caveats: this is pre-tax, and it can't price the things that don't fit in a spreadsheet — an index fund never needs a new roof, but it also never lets you add value with a renovation. For the full property view see the rental property ROI calculator.
This calculator compares two paths for the same cash: buy a rental and reinvest any positive cash flow, or invest the down payment elsewhere and cover any shortfall from that same alternative account. At national-median price and rent, financed at 6.71% with 2.9% rent growth against an illustrative 7% alternative return, the property reaches $101,849 in five years while the alternative reaches $132,100 — a $30,251 advantage for staying invested elsewhere, entirely because every year of this deal's cash flow was negative and had to be funded out of pocket rather than compounding.
How the comparison is built to be symmetric
The calculator runs the same year-by-year pro forma as the rental ROI tool, then splits each year's cash flow into two cases and treats both consistently at the same alternative rate of return. If a year's cash flow is positive, it is reinvested at your entered alternative rate from that year to the end of the hold. If a year's cash flow is negative, that shortfall is treated as money you would otherwise have put into the alternative investment — so it is added to the alternative side, compounding from that year forward too. Both paths compound at the identical rate — the only difference is which asset is holding the money in which year. That symmetry is what makes this a fair comparison of the true opportunity cost of the down payment, rather than a comparison that quietly favors one side.
At the end of the hold, the property side totals net sale proceeds plus all reinvested positive cash flow; the alternative side totals the original cash invested grown at the alternative rate, plus every funded shortfall grown at that same rate from when it was needed. The gap between the two is the advantage (or disadvantage) of buying, in dollars — and the calculator also reports each side's compound annual growth rate for a like-for-like percentage comparison.
Worked example — national medians against a 7% alternative
Same base inputs as the ROI calculator's worked example: $343,800 purchase price and $1,531 monthly rent (Census Bureau Q2 2026 medians), 25% down ($85,950 cash invested), 6.71% Freddie Mac rate, 7.3% Census vacancy, 2.9% BLS CPI rent growth, 0% appreciation, 0% expense inflation and selling costs (no verified figures), 5-year hold. The alternative return is the one number this calculator asks the user to supply directly — there is no verified national figure for "the return an alternative investment would earn," so this example uses an illustrative 7% purely to show the mechanics; substitute your own expectation.
As compound annual growth rates: the property path returns 3.45% a year on the $85,950 invested; the alternative path returns 8.98% — higher than the 7% input rate because it also captures the return earned on the out-of-pocket shortfalls the property would have required each year. This is the calculator's honest way of pricing what a negative-cash-flow property actually costs an investor beyond the sticker price of the down payment.
The one input that decides the comparison
The alternative return rate is the single input that moves this comparison the most, because it compounds on both sides of the ledger simultaneously — it is applied to the alternative investment's growth and to every dollar of property shortfall funded from that same source. A lower alternative rate (say 4%) narrows or can flip the gap in the worked example above; a higher one widens it further. Because no verified figure exists for what an alternative investment will actually return over a specific future hold period, this is the assumption most worth stress-testing across a realistic range rather than entering once and treating as settled.
The financing rate matters almost as much, for the same reason it dominates the plain cash-flow calculators: it sets the fixed debt service that determines whether any year's cash flow is positive (reinvested and compounding on the property side) or negative (funded and compounding on the alternative side instead). A lower rate can flip individual years from negative to positive, which changes which side of the ledger that year's dollars compound on — not just the year's cash-flow total.
What this comparison leaves out
- ·Taxes on either side. Neither the property's cash flow and sale proceeds nor the alternative investment's growth are adjusted for taxes. Depreciation specifically would improve the after-tax property case; see the rental depreciation calculator for that separate math under IRS Publication 527.
- ·Liquidity and volatility differences. A dollar in a diversified alternative investment and a dollar of home equity are not equally liquid or equally risky; this comparison treats both as certain compounding at the entered rate.
- ·Non-financial reasons to own. Control over the asset, forced savings discipline, and leverage on future purchasing power are real considerations this dollar-for-dollar model does not weigh.
Methodology
The worked example runs this calculator's own year-by-year comparison at the Census Bureau's Q2 2026 median asking sale price ($343,800) and median asking rent ($1,531), the same release's 7.3% national rental vacancy rate, the Freddie Mac PMMS 30-year rate for the week ending September 3, 2026 (6.71%), and the BLS CPI Rent of Primary Residence twelve-month rent-growth figure (2.9%) as the rent-growth input. The 7% alternative-return input is illustrative — no verified national figure exists for a specific future investment return — and is disclosed as such throughout.
Sources
- US Census Bureau — Housing Vacancy Survey, Q2 2026 — accessed 2026-09-07
- US Bureau of Labor Statistics — CPI News Release, Rent of Primary Residence — accessed 2026-09-07
- Freddie Mac — Primary Mortgage Market Survey — accessed 2026-09-07
- IRS — Publication 527, Residential Rental Property — accessed 2026-09-07
Property vs an unlevered alternative: the structural trade-offs
| Factor | Rental property | Alternative investment |
|---|---|---|
| Leverage | Appreciation compounds on full value | Returns on cash invested only |
| Debt paydown | Tenants build your equity | None |
| Transaction costs | Several % to buy and to sell | Near zero |
| Liquidity | Months to sell | Days |
| Effort | Tenants, repairs, management | Passive |
Leverage is why property can beat a higher-returning alternative — and why it magnifies losses just as efficiently. Pre-tax comparison.
Frequently asked questions
How is this different from a normal rent vs buy calculator?
A consumer rent-vs-buy calculator asks whether you should buy the home you live in instead of renting it. This is the investor version: it asks whether buying a rental property to let out beats simply investing the same capital somewhere else. The question isn't housing — it's what your money should be doing. That makes the opportunity cost of your down payment the central variable rather than an afterthought.
What is the opportunity cost of a down payment?
It's the return your down payment would have earned if you hadn't tied it up in a property. A rental that returns 6% a year isn't obviously good or bad in isolation — it depends entirely on what else that capital could have done. If an alternative investment would have returned 8%, the property is destroying value relative to the alternative despite showing a positive return. Most rental calculators ignore this comparison entirely.
Why does property often win despite low rental yields?
Leverage. When you put 25% down, your appreciation compounds on the full property value, not just the capital you contributed — so 3% appreciation on the whole asset is roughly 12% on your down payment before costs. Add tenant-funded mortgage paydown, which quietly converts debt into equity, and property can beat an unlevered alternative even with modest yields. The flip side is that leverage magnifies losses just as efficiently.
How does this comparison stay fair?
Both paths compound at the same alternative rate. The property path reinvests each year's positive cash flow at that rate; the alternative path receives not just the initial capital but also any money you'd have spent covering the property's negative cash flow. Without that symmetry the comparison would quietly flatter one side — a common flaw in property-versus-market arguments.
Why does the hold period change the answer so much?
Real estate carries heavy transaction costs — several percent to buy and several more to sell — which punish short holds badly. An index fund has almost none. But over a long hold, leverage, mortgage paydown, and rent growth compound in property's favour while those one-time costs amortise away. The answer frequently flips somewhere in the middle, which is why it's worth testing several horizons rather than trusting a single number.
Does this include taxes?
No — it's a pre-tax comparison. Tax treatment varies enormously by investor and jurisdiction: depreciation, how rental losses offset other income, capital gains on sale, and the tax on investment gains all depend on personal circumstances. Modelling it generically would create false precision. Use the dedicated depreciation and capital-gains tools for the tax layer, and speak to a professional.