How to Underwrite a Duplex: A Beginner’s Guide to Smarter Real Estate Investing
- Obafemi Mojisola
- Jun 10, 2025
- 2 min read
Thinking of investing in a duplex?
Smart move. Duplexes offer a great entry point into multifamily investing, cash flow potential, low owner-occupancy requirements, and scalable returns.
But before you make an offer, you need to underwrite the deal like a pro. In this guide, we’ll walk you through how to analyze a duplex step by step to determine if it’s a smart investment or a financial trap.
What Does “Underwriting” Mean?
In real estate investing, underwriting is the process of analyzing a property's numbers to determine if it will generate a positive return based on your goals.
Think of it as a financial check-up for your deal. It helps you spot red flags, negotiate better, and protect your capital.,
Step-by-Step: How to Underwrite a Duplex
1. Determine Projected Rental Income
Start with market rent research:
Check Zillow, Rentometer, or local MLS for similar duplex units
Be conservative — use the lower end of the rent range
Consider seasonal trends and vacancy risk
Example: If each unit rents for $2,000/month → Total Gross Rent = $4,000/month
2. Account for Vacancy
Even the best properties have empty months.
Use a standard 5–8% vacancy rate
Multiply gross rent by (1 - vacancy rate)
🧮 $4,000 × 0.92 (8% vacancy) = $3,680 effective monthly income
3. Estimate Operating Expenses
A good rule of thumb: 35%–50% of gross income will go toward expenses.
Break it down:
Expense Type | Estimate |
Property Taxes | Use county records |
Insurance | Get a quote |
Repairs/Maintenance | 5–10% of rent |
Property Management | 8–10% of rent (if outsourced) |
Utilities (if owner pays) | $100–$300/month/unit |
Capital Reserves | Save for big-ticket items (roof, HVAC) |
Add all these to find Total Operating Expenses
4. Subtract Expenses from Income (Net Operating Income - NOI)
NOI = Effective Gross Income – Operating Expenses
This is your property’s true income, before financing costs.
5. Factor in Financing (if applicable)
Use your mortgage terms to calculate monthly payments
Subtract your loan payment from NOI to get Cash Flow
Positive Cash Flow = Green Light
6. Run the Key Investment Metrics
Here are the essential numbers every investor should know:
Cash-on-Cash Return(Annual Cash Flow ÷ Cash Invested)Target: 8%–12%
Cap Rate(NOI ÷ Purchase Price)Target: 5%–7% (varies by market)
Debt Service Coverage Ratio (DSCR)(NOI ÷ Annual Debt Payments)Target: 1.25+
Bonus Tips
Use an underwriting template or software (Vestora provides one to clients)
Always review local rent control or zoning laws
Run your numbers with pessimistic and optimistic scenarios
Final Thoughts
Underwriting a duplex isn’t just about crunching numbers. It’s about understanding your risk, your returns, and your goals.
When you work with Vestora, we help you:
Break down the numbers clearly
Use our proven duplex underwriting model
Evaluate real deals together on live Zoom calls
Ready to underwrite your next deal with confidence?
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