Investment Comparison Tool

How to compare rental deals side by side

To compare two rental properties fairly, put both on the same assumptions: the same vacancy method, a realistic capital-expenditure reserve for each, and identical financing terms. Then read five numbers together, not one: cash flow, cap rate, cash-on-cash return, debt service coverage (DSCR) and total return. The deal that wins on most of them, and still holds up when you stress the rent and vacancy, is usually the better buy.

The comparison tool above helps with the bigger structural choices: entity type, loan type, management approach and overall strategy. This guide covers the property-level comparison that comes before those decisions, with a worked example using two hypothetical properties and the full arithmetic.

The five metrics that matter

1. Net operating income and cash flow

Net operating income (NOI) is rent collected minus operating expenses: taxes, insurance, repairs, management, vacancy and a capital reserve. It excludes the mortgage. Cash flow is NOI minus debt service (principal and interest). Cash flow is what you actually live with month to month, but it depends on how you finance the deal, so it is a poor way to compare the properties themselves.

2. Cap rate

Cap rate is NOI divided by purchase price. Because it ignores financing, it is the cleanest way to compare two properties at different prices. A $180,000 house with $12,078 of NOI has a 6.71% cap rate. The weakness: cap rate only tells you as much as the NOI estimate behind it. A seller’s cap rate that leaves out vacancy, management or capital reserves will look one to three points better than reality.

3. Cash-on-cash return

Cash-on-cash return is annual cash flow divided by total cash invested (down payment, closing costs and any up-front repairs). It answers the question “what is my cash earning this year?” It is useful for comparing a rental against other uses of the same money, but it ignores loan paydown and appreciation, and it changes dramatically with leverage. Our ROI formulas cheat sheet lists the exact formulas.

4. Debt service coverage ratio (DSCR)

DSCR is NOI divided by annual debt service. At 1.00 the rent exactly covers the mortgage after expenses; at 1.25 there is a 25% cushion. DSCR is the best single measure of how fragile a leveraged deal is, and it is the number DSCR lenders underwrite against, so it also tells you how financeable the property is.

5. Total return

Total return adds the other ways a rental builds wealth: cash flow, principal paydown (your tenants paying down the loan) and appreciation. Tax effects such as depreciation can be added too, but they depend on your income and are best modelled separately. Total return is the most complete number and also the easiest to fool yourself with, because the appreciation input is a guess. Always look at it with zero appreciation first.

Normalising for different prices and leverage

The most common comparison error is letting financing decide the winner. If one property is quoted with 20% down and the other with all cash, their cash-on-cash returns are not comparable. To compare like with like:

• Compare the properties unlevered first. Cap rate and expense ratio (operating expenses as a percentage of gross rent) show which asset is better, independent of the loan. The expense ratio calculator helps check whether a seller’s expenses are plausible.
• Then apply identical financing. Same down payment percentage, interest rate and term for both. Now cash-on-cash and DSCR differences come from the properties, not the loans.
• Account for the cash you don’t spend. If property A needs $39,200 less cash than property B, that money either sits as reserves, goes toward a second property, or earns something elsewhere. Include it.
• Check whether leverage helps at all. Divide annual debt service by the loan amount to get the loan constant. If the cap rate is below the loan constant, borrowing lowers your cash return (negative leverage). At 7% over 30 years the loan constant is about 7.98%, so a 6.7% cap rate property earns less on your cash with the loan than without it, in year one.

Risk factors the headline numbers hide

Vacancy and tenant turnover

Use local evidence (how long comparable units take to rent, and typical tenancy length for the property type) rather than a national percentage. A multi-unit property spreads vacancy risk: one empty unit in a duplex halves income instead of zeroing it. But it also doubles turnover work. The rent estimator is a starting point for checking that the projected rent is realistic.

Capital expenditures

Roofs, HVAC systems, water heaters, windows, sewer lines and driveways wear out on a schedule. Two properties with identical NOI before reserves can be very different investments if one has a 22-year-old roof. List each major component, estimate its remaining life and replacement cost, and divide. That number, not a generic percentage, belongs in the comparison. A thorough due diligence checklist and a professional inspection are how you get those inputs.

Location and regulation

Location affects demand, rent growth, insurance costs, property tax reassessment and the pool of future buyers. It also determines the legal environment: rent regulation, registration and inspection programs, and eviction timelines vary by state and city. Check the relevant pages in our state legal guides and the local ordinances before treating two cities as interchangeable.

Concentration and liquidity

One expensive property concentrates risk in one roof, one neighbourhood and one sale. Two cheaper properties diversify but add management overhead. Liquidity matters too: a property type with a thin buyer pool may take longer to sell when you want to exit.

Worked example: a single-family house vs a duplex

Example (hypothetical): Property A is an older single-family house at $180,000 renting for $1,950 a month. Property B is a newer duplex at $320,000 with two units at $1,650 each ($3,300 a month). Both are financed at 75% loan-to-value, 7% interest, 30 years, with closing costs of 3% of price. Vacancy, maintenance and management use the same percentages for both. The capital reserve is 10% of rent for A because its roof and HVAC are near the end of their lives, and 6% for B. All figures are illustrative.

How the numbers were worked out

For A: $23,400 of rent minus $11,322 of expenses gives NOI of $12,078, and $12,078 ÷ $180,000 = 6.71%. The $135,000 loan at 7% over 30 years costs $898.16 a month, or $10,778 a year. Cash flow is $12,078 − $10,778 = $1,300, and $1,300 ÷ $50,400 = 2.58% cash-on-cash. DSCR is $12,078 ÷ $10,778 = 1.12. In year one, about $1,371 of the payments reduce principal. Add 3% appreciation ($5,400) and the total return is $1,300 + $1,371 + $5,400 = $8,071, or 16.01% of the cash invested.

For B: $39,600 − $17,984 = $21,616 NOI, a 6.75% cap rate. The $240,000 loan costs $1,596.73 a month ($19,161 a year), leaving $2,455 of cash flow, 2.74% on $89,600. DSCR is 1.13. Principal paydown is about $2,438, and 3% appreciation is $9,600, for a total of $14,493, or 16.18%.

Stress test

On the base case the two are nearly identical, so the decision comes down to resilience. If vacancy doubles to 12%, A’s cash flow falls by $1,404 to −$104 a year, while B’s falls by $2,376 to +$79. If market rent drops 10% (with vacancy and management scaling down with it), A loses $1,989 of NOI and goes to −$689, and B loses $3,366 and goes to −$911. Break-even occupancy (the share of scheduled rent needed to cover expenses and the mortgage) is 88.4% for A and 87.8% for B. Neither deal has much margin. Both cap rates sit below the 7.98% loan constant, so both are examples of negative leverage at these terms.

What the example shows

The headline metrics cannot separate these two. What can: A needs $39,200 less cash, which could be held as a reserve for its ageing roof. B has two income streams and newer systems but more dollars at risk if rents soften. An investor with limited cash and a tolerance for hands-on repairs might prefer A plus a large reserve; one who values steadier occupancy might prefer B. Either way, the honest answer is that neither clears a comfortable DSCR at 75% leverage and 7%, and a larger down payment or a lower price would be needed for real cushion. The financing calculator shows how the down payment changes these numbers.

A decision framework

1. Screen on cap rate using your own expense estimates, not the listing’s. Drop anything that only works on the seller’s numbers.
2. Apply your real financing identically to both and set a minimum DSCR you are comfortable with. Many small landlords choose a cushion of 1.20 or more for their own safety margin.
3. Stress both deals: vacancy doubled, rent down 10%, one major capital item in year one, and rates one point higher if the loan is adjustable or you plan to refinance.
4. Compare total return at 0% appreciation, then at a modest rate. If the winner changes only with appreciation, treat that as a bet, not a margin.
5. Weigh the risks the spreadsheet doesn’t: your time, distance, the regulatory environment, and how easily you could sell.
6. Decide what the leftover cash does. Reserves are a legitimate use, not idle money.

For a full single-property workup before you compare, use the property analysis worksheet or the property investment analyzer.

Common mistakes when comparing rentals

• Comparing pro forma rents with actual rents. One listing shows current leases, the other shows what the seller thinks the units could rent for. Use the same basis for both.
• Leaving out capital reserves or management. Even if you self-manage, include management at a market rate so your time has a cost and the comparison survives if you hire a manager later.
• Ignoring closing costs and up-front repairs in cash invested, which inflates cash-on-cash.
• Treating appreciation as income. It is not spendable until you sell or refinance, and it can be negative.
• Forgetting the exit. The way you eventually leave a property (sale, exchange or holding long term) changes its after-tax return. The keep-or-sell calculator compares those exits for a property you already own.

Related tools and guides

• Rental ROI calculator
• Multi-unit property calculator
• Break-even calculator
• How to calculate ROI on rental properties
• Property investment due diligence guide

All examples are hypothetical and for education only. They are not investment, lending or tax advice. Verify rents, expenses and loan terms for any real property and consult a qualified professional before buying.