How to do a duplex cash flow analysis

This step-by-step workflow walks you from estimated rents through pre-tax monthly cash flow and three core metrics: cap rate, cash-on-cash return, and debt service coverage ratio, or DSCR. Follow each stop point, plug your numbers into a spreadsheet, and pause after any step to re-run assumptions. The formulas and sensible input ranges below let you judge whether a duplex fits your investment goals.

Step 1: estimate gross scheduled rent for both units

Gross scheduled rent is the total monthly rent you expect to collect if both units are leased at market rates. Use this process:

• Gather recent rental listings and active comps in the same neighbourhood and unit type rather than relying only on advertised asking prices. Local market pages and map-based searches speed this step.
• Adjust for condition and included utilities. If the owner pays heat or water, reduce the effective rent relative to comparables where tenants pay utilities.
• If you plan to live in one unit, decide whether to treat that unit as market rent for valuation or as a reduced personal housing cost for your cash flow model. Owner-occupancy also affects financing rules and monthly debt service.

Formula, monthly: Gross scheduled rent = Rent unit A + Rent unit B. For a conservative base case, collect at least three comparables per unit and use the median rent. For method examples and the recommended calculation order, see this duplex cash-flow walkthrough (external resource).

(Reference: Mason duplex cash flow: step-by-step.)

Step 2: calculate effective gross income (EGI) — apply vacancy and concessions

EGI accounts for vacancy, turnover downtime, and concessions you might offer. The formula is:

EGI = Gross scheduled rent − vacancy and concessions

Run sensitivity tests rather than relying on a single vacancy rate. Use three scenarios: conservative (higher vacancy), base (market median), and optimistic (low vacancy). Document the percentage used for each scenario so you can compare outcomes objectively.

Step 3: list operating expense categories and apply realistic ranges

Operating expenses reduce EGI to net operating income. Build a line-item budget that separates recurring from irregular costs. Typical categories include:

• Property tax
• Insurance, landlord policy
• Utilities paid by the owner, such as heat, water, or electricity
• Repairs and maintenance
• Property management fees if you hire a manager
• Advertising and tenant screening
• Legal and accounting fees
• Vacancy allowance and turnover repairs
• Capital expenditures, funded to a reserve

As a rule of thumb, operating expenses often consume a significant share of gross rental income. A commonly used range is roughly 35 percent to 50 percent of gross rental income depending on property age, condition, and how many utilities the owner pays. Use that band to sanity-check your line-item totals and to build conservative and optimistic expense scenarios (source: DuplexForSale).

(Reference: How to analyse a duplex investment property.)

Expense details and common pitfalls

Model one-time costs, such as immediate repairs after purchase, separately from recurring monthly costs. For capital expenditures, budget an annual reserve converted to a monthly amount so your monthly cash flow reflects long-term ownership costs. Common mistakes include skipping capex, understating vacancy costs, or using advertised rents without adjusting for owner-paid utilities.

Step 4: compute net operating income (NOI)

NOI is the operating profit before debt service and taxes. Formula:

NOI = Effective gross income − operating expenses

Keep NOI separate from financing. That separation helps you compare properties regardless of how you fund them. Using NOI for cross-property comparison is standard practice in duplex analysis.

Step 5: add financing costs to reach pre-tax cash flow

To convert NOI into owner cash flow, subtract debt service. Required loan inputs are:

• Purchase price
• Down payment amount and percent
• Loan amortization period
• Interest rate
• Payment frequency, normally monthly

Compute the annual mortgage payment from the loan inputs and divide by 12 for monthly debt service. Then:

Pre-tax monthly cash flow = NOI − monthly debt service

Owner-occupant financing can change minimum down payment, amortization rules, or available rates, which alters monthly debt service and cash flow. Always verify owner-occupancy rules with a mortgage specialist before finalising assumptions. Use a mortgage calculator to convert interest and amortization inputs into monthly payments when populating your spreadsheet.

Financing inputs, sensitivity checks, and starter scenarios

Test at least three scenarios: conservative, base, and optimistic. Change vacancy, expense percentages, and interest rate in each run. Useful sensitivity checks include interest rate plus or minus one percentage point, down payment plus or minus five to ten percentage points, and a capex shock representing a one-time major repair. If a conservative scenario produces persistent negative cash flow or a DSCR that barely covers debt service, pause and re-evaluate purchase price, financing, or rent assumptions.

Step 6: calculate key investment metrics — cap rate, cash-on-cash return, DSCR

Compute these standard metrics to compare deals and set decision thresholds. Formulas and plain-language definitions follow:

• Cap rate = NOI / purchase price, annualised. Cap rate shows asset yield independent of financing.
• Cash-on-cash return = annual pre-tax cash flow / total cash invested, where total cash invested equals down payment plus closing costs. This metric shows the cash yield on your invested capital.
• DSCR = NOI / annual debt service. DSCR under 1.0 means NOI does not cover debt service, so many investors require a buffer above 1.0 to account for unexpected costs.

Each metric answers a different question. Use cap rate to assess asset-level yield, cash-on-cash to measure investor cash return, and DSCR to verify debt coverage. Use all three together for a balanced decision.

(Additional method notes: see the step-by-step duplex cash-flow approach in the external reference.)

Edmonton-specific considerations for duplex investors

In Edmonton, duplexes often outperform single-family rentals on cash flow because two rental incomes help offset fixed costs and vacancy risk. Local checks to run include recent rent comps in the exact neighbourhood, current vacancy trends, the property tax rate, and any zoning or licensing rules that affect multi-unit homes. For a local perspective on duplex advantages, see the regional comparison article.

(Reference: Duplex versus single-family rentals in Edmonton.)

Decision criteria, stopping points, and mistakes to avoid

Before you make an offer, run this checklist:

• Does the conservative scenario produce non-negative pre-tax monthly cash flow after debt service?
• Is DSCR comfortably above 1.0, with a preferred buffer you set for safety?
• Does the cash-on-cash return meet your minimum target for this deal type?
• Have you reserved monthly amounts for capex and unexpected repairs?
• Are your rent estimates supported by at least three local comparables?

Frequent mistakes include understating operating expenses, using gross rents without utility adjustments, ignoring capital reserves, and failing to stress-test financing assumptions.

Tools, spreadsheet template, and how to run three-scenario analysis

Create a spreadsheet with input fields for unit rents, vacancy percentage, line-item operating expenses, purchase price, down payment, interest rate, and amortization. Calculated fields should include EGI, NOI, monthly debt service, pre-tax cash flow, cap rate, cash-on-cash, and DSCR. Run conservative, base, and optimistic scenarios by varying vacancy, expenses, and interest.

Map each spreadsheet field to the steps above so you can show a lender or partner exactly how assumptions change results. If you prefer an automated loan conversion, use a mortgage calculator to pre-fill debt-service numbers for the sheet.

Next step: get a local duplex suitability review

If you want a populated spreadsheet with local comparables and a short suitability memo for a specific Edmonton duplex, request a duplex suitability review. Anand Realty can pull MLS-based comparables, populate rent and expense fields for your property, and walk through the three-scenario analysis in a complimentary consult. Book a review or request more information at ANAND REALTY INC.

Frequently asked questions

What inputs do I need to run a duplex cash flow analysis?

At minimum, you need projected rents for both units, a vacancy percentage, a line-item operating expense budget, the purchase price, your intended down payment, interest rate, and amortization period. With those inputs you can calculate EGI, NOI, and pre-tax cash flow.

How much vacancy and operating expense allowance should I plan for?

There is no single correct number. Use a base-case vacancy that reflects the neighbourhood and run conservative and optimistic scenarios. For operating expenses, compare your line-item total to a rule-of-thumb band, such as 35 percent to 50 percent of gross rental income, and stress-test expenses in a conservative scenario.

How does owner-occupancy financing change the down payment and cash flow?

Owner-occupancy can change lender rules for minimum down payment, amortization, and sometimes available interest rates. Those changes affect monthly debt service and therefore cash flow. Confirm owner-occupancy rules with a mortgage specialist and model both owner-occupied and investor financing scenarios before committing.

Which metric should I prioritise: cap rate or cash-on-cash return?

Neither metric alone is decisive. Cap rate is useful to compare asset earning power independent of financing. Cash-on-cash return shows the cash yield on the money you actually invest. Use both metrics along with DSCR to judge whether a property fits your objectives.

When should I call a REALTOR® or mortgage specialist during the analysis?

Engage a REALTOR® early for local rent comps, property history, and an opinion on expected maintenance costs. Contact a mortgage specialist when you have a purchase price and down payment in mind so you can model realistic debt service. Anand Realty can help with local comparables and a populated spreadsheet for your review.

External references and further reading: Mason duplex cash flow guide, DuplexForSale analysis, Edmonton duplex versus single-family overview.

Talk with ANAND REALTY INC

Contact ANAND REALTY INC to ask about the next step and confirm which options fit your needs.