This framework is designed for a single-family rental, fixer, duplex, triplex, or fourplex. One to four residential units can generally fit residential-mortgage channels; five or more units are generally treated as commercial multifamily. The economic analysis, however, should always treat the property like a business.
1. Verify what physically and legally exists
Count legal units, bedrooms, parking, meters, and permitted improvements. Read leases and estoppels; inspect roof, foundation, drainage, electrical, plumbing, HVAC, sewer/septic, safety, and insurance availability. An unpermitted “unit” should not be underwritten as dependable income.
2. Build believable income
Start with signed lease rent, then compare market rent using truly similar properties. Subtract vacancy, concessions, bad debt, and turnover. Add laundry, parking, or utility reimbursements only if legal, documented, and likely to continue.
3. Rebuild every expense
Include taxes after sale, insurance quotes, management even if self-managing, repairs, landscaping, owner-paid utilities, licensing, HOA, accounting, pest control, and a capital reserve. Separate operating expenses from debt service and income tax so NOI remains comparable.
Illustrative duplex
| Gross scheduled rent | $48,000 |
| Vacancy/credit loss (5%) | −$2,400 |
| Effective income | $45,600 |
| Operating expenses + reserve | −$18,600 |
| NOI | $27,000 |
| Annual debt service | −$22,200 |
| Pre-tax cash flow | $4,800 |
4. Underwrite the fixer twice
Analyze the property “as is” and “as stabilized.” Build a written scope by trade; add permits, design, dumpsters, utilities, financing interest, insurance, taxes, theft, lease-up time, and contingency. Sweat equity can create value—painting, clean-up, landscaping, or skilled work—but do not price your labor at zero or perform regulated work without proper licensing and permits.
5. Model the actual financing
Use the loan amount, rate, amortization, mortgage insurance, points, closing costs, reserves, and any balloon or prepayment penalty. Owner-occupying a 2–4 unit property can open different products than buying it strictly as an investment. A rental DSCR loan may qualify chiefly from rent coverage, but can carry different rates, fees, prepayment terms, and reserve requirements.
6. Read several metrics together
Cap rate compares NOI to price without financing. DSCR compares property cash flow to debt service. Cash-on-cash compares spendable annual cash flow to your contributed cash. Break-even occupancy shows how much income can disappear before operations and debt are uncovered. None replaces inspection, liquidity, or judgment.
Open the interactive investment metrics calculator →
7. Stress-test the story
Change four assumptions
Reduce rent 5%; increase vacancy; raise insurance and repairs; add 10%–20% to the rehab; delay completion; and test a refinance or sale at a higher cap rate. If one modest change destroys the deal, the price or debt is too aggressive.
8. Write the decision in one page
State purchase price, all cash required, verified income, normalized expenses, immediate work, base/downside/upside cash flow, financing risks, and at least two viable exits. Then list facts still unverified. A disciplined “no” is a profitable outcome when it prevents a bad purchase.
Further reading: Investor terminology · BRRRR method · Fannie Mae rental-income documentation ↗ · IRS Publication 527 ↗
Educational only, not legal, tax, lending, construction, appraisal, or investment advice. Figures are illustrative.