Key takeaways
- Cash flow is rent minus vacancy minus all operating expenses minus debt service — not rent minus mortgage.
- Budget 8% to 12% of rent for maintenance and capital reserves combined, even on new construction.
- Cash-on-cash return measures the deal; total return adds principal paydown, appreciation, and tax benefits.
- The purchase price is set the day you buy. Everything else can be improved.
Build the income line honestly
Start with market rent, verified against actual leased comparables rather than asking rents on listing sites. Asking rents are aspirations; leased rents are facts. Then apply a vacancy factor — 5% to 8% in most stable markets, higher in markets with heavy turnover or seasonal demand.
Add ancillary income where it genuinely exists: pet rent, parking, storage, laundry, utility billbacks. On single-family rentals this is usually modest. On small multifamily it can add 3% to 8% of gross revenue and is frequently the easiest value-add available to a new owner.
The expenses that sink first-time investors
The predictable expenses are easy: property tax, insurance, HOA, and management. The ones that destroy pro formas are maintenance and capital expenditures. Maintenance is the ongoing cost of keeping a property functional. CapEx is the replacement reserve for roofs, HVAC systems, water heaters, flooring, and appliances — all of which have finite lives and will fail on your watch if you hold long enough.
Reserve 4% to 6% of rent for maintenance and another 4% to 6% for CapEx. New construction still needs CapEx reserves; a roof installed today is simply a roof that fails in year 25. Skipping these reserves does not make a deal profitable, it makes the loss arrive later and all at once. Our cash flow calculator models all of this.
Financing changes the deal, not the property
Investment property financing requires more down — typically 20% to 25% on conventional loans — and prices worse than owner-occupied. DSCR loans qualify on the property's income rather than your personal income, which is useful for investors with multiple properties or complex tax returns, at the cost of a higher rate.
House hacking sidesteps this entirely. Buying a two- to four-unit building with an FHA or conventional low-down-payment loan, living in one unit for a year, is the single most capital-efficient entry into rental ownership available to most people.
Which return metric to trust
Cap rate measures the property independent of financing and is the right tool for comparing assets. Cash-on-cash return measures your actual return on invested cash and is the right tool for comparing deals. Total return adds principal paydown, appreciation, and tax benefits, and is the right tool for comparing real estate against other asset classes.
Use all three, and be honest about which assumptions are doing the work. A deal that only clears your return threshold under 5% annual appreciation is an appreciation bet wearing a rental costume.
Where the actual risk lives
The risks that materially damage rental investors are concentrated: a bad tenant placement causing months of lost rent and damage, a major capital failure without reserves, an insurance or tax reassessment jump after purchase, and buying at a price that leaves no margin.
Screening discipline addresses the first, reserves address the second, and conservative underwriting addresses the third and fourth. Read tenant screening before you place anyone in a unit.
Frequently asked questions
What is the 1% rule?
A screening heuristic suggesting monthly rent should equal at least 1% of purchase price. In most metros today it filters out nearly everything, which limits its usefulness. Treat it as a fast first filter, never as underwriting.
Should I buy in my own market or out of state?
Local ownership gives you knowledge and control. Out-of-state investing gives access to better yields but requires genuinely trustworthy management, which is the hardest thing to source remotely.
How many properties do I need to quit my job?
Divide your target income by realistic per-door net cash flow after all reserves. The result is usually a larger number than people expect, which is why most investors focus on equity growth rather than early cash flow.
Sources & further reading
- Federal Reserve, Survey of Consumer Finances housing wealth data
- National Apartment Association operating expense benchmarks
- Fannie Mae Selling Guide, Investment Property Eligibility
Figures and rules change. Verify current requirements with the issuing agency or a licensed professional before acting.