Multi-Family Property Numbers That Matter: A Boston Investor Math Breakdown

Most articles about multi-family investing in Boston tell you to “run the numbers” without actually showing you what those numbers look like. This article skips the advice and goes straight to the arithmetic. Every calculation below uses real Greater Boston price points, actual expense figures, and the specific cost line items that Massachusetts landlords face but investors in other markets never see. Pull up a spreadsheet and follow along.

Cap Rate on a Real Boston Triple Decker: The Actual Math

Cap rate is Net Operating Income divided by purchase price. Simple formula, but investors routinely botch it by using gross rent instead of net income. Here is a worked example using a triple decker in Dorchester priced at $1,050,000 with three units each renting at $2,200 per month.

Gross annual rent: $2,200 x 3 units x 12 months = $79,200

Now subtract vacancy. Boston multi-family vacancy historically runs 5 to 7 percent on a stabilized property. Use 6 percent: $79,200 x 0.06 = $4,752 vacancy allowance. Effective gross income = $74,448.

Operating expenses on a 1900s era Dorchester three family typically look like this annually: property taxes $9,800, insurance $4,200, water and sewer $3,600 (Boston water rates are among the highest in the country), snow removal $2,400, landscaping and exterior maintenance $1,800, property management at 8 percent of collected rents $5,956, repairs and capital reserves $6,000, miscellaneous $800. Total operating expenses = $34,556.

Net Operating Income = $74,448 minus $34,556 = $39,892.

Cap rate = $39,892 divided by $1,050,000 = 3.80 percent.

That number will surprise investors coming from markets like Cleveland or Indianapolis where cap rates of 7 to 9 percent are common. Greater Boston consistently trades in the 3.5 to 5 percent range on residential multi-family, which means your income cushion is thin and every expense line matters enormously. You can review current transaction benchmarks at Boston Housing Data to calibrate your expectations before writing any offer.

The One Percent Rule and Why It Fails in Greater Boston

The one percent rule says your monthly rent should equal at least one percent of the purchase price. On that same Dorchester triple decker at $1,050,000, one percent monthly rent would require $10,500 per month total, or $3,500 per unit.

Market rent for comparable units in Dorchester runs $2,100 to $2,400. You are collecting $6,600 per month, not $10,500. The property hits 0.63 percent, and that is actually a competitive deal by Boston standards.

The one percent rule was calibrated for lower-cost markets. It breaks completely in any high-barrier coastal city. Boston investors who apply it mechanically will never buy anything. The more useful local benchmark is whether the property cash flows at all after debt service, which is a different and more honest question. To understand which neighborhoods offer even marginally better rent-to-price ratios, spend time with the Boston Neighborhood Finder and compare East Boston, Hyde Park, and Mattapan against Somerville or Cambridge before assuming location does not matter to your math.

Cash on Cash Return: A Step by Step Calculation

Cash on cash return measures the annual pre-tax cash flow you receive divided by the actual cash you invested. It is the number that tells you what your money is earning, not your lender’s money.

Using the same triple decker, assume a 25 percent down payment on a $1,050,000 purchase price plus closing costs.

Down payment: $262,500. Closing costs in Massachusetts typically run 2 to 3 percent on the buyer side including attorney fees, title insurance, recording fees, and lender fees. Use 2.5 percent: $26,250. Total cash invested at closing: $288,750.

Now calculate annual debt service. Loan amount = $787,500. At a 7.25 percent interest rate on a 30 year amortizing investment property loan, monthly principal and interest = approximately $5,373. Annual debt service = $64,476.

Annual cash flow before taxes = NOI minus debt service = $39,892 minus $64,476 = negative $24,584.

This property cash flows negative at current Boston pricing and a 25 percent down payment at current rates. Cash on cash return = negative $24,584 divided by $288,750 = negative 8.5 percent.

This is not a failure of analysis. It is the honest result. Most Boston multi-family buyers at today’s prices are banking on appreciation, principal paydown, and eventual rent growth rather than immediate cash flow. Understanding this math before you buy prevents shock after closing. Before committing to a loan structure, use a tool like Compare Mortgage Rates to find the most competitive investment property financing available, because shaving 0.25 percent off your rate reduces annual debt service by roughly $1,600 on an $787,500 loan.

Vacancy and Maintenance Reserves: What Boston Investors Actually Need

Generic investing guides suggest 5 percent for vacancy and 5 percent for maintenance. Those numbers are dangerously low for Boston multi-family.

Vacancy Reserve Calculation

A realistic Boston triple decker experiences one unit turnover roughly every 14 to 18 months per unit. Each turnover costs you one month vacancy plus $800 to $1,500 in turnover expenses including cleaning, minor repairs, and advertising. On three units with 16-month average tenancy, you average 2.25 turnovers per year. Each costs roughly one month rent ($2,200) plus $1,150 average turnover cost = $3,350 per turnover. Annual vacancy and turnover cost = 2.25 x $3,350 = $7,538. As a percentage of gross rent: $7,538 divided by $79,200 = 9.5 percent. Not 5 percent.

Maintenance Reserve Calculation

Boston triple deckers were built overwhelmingly between 1890 and 1930. Capital expenditures on a 100 year old wood-frame building follow a predictable cycle. Roof replacement at $18,000 every 20 years = $900 per year. Boiler replacement at $8,000 every 15 years = $533 per year per unit, so $1,599 for three units. Exterior painting at $12,000 every 8 years = $1,500 per year. Window replacement at $600 per window with roughly 24 windows every 25 years = $576 per year. Plumbing and electrical on a building this age: budget $2,400 per year conservatively. Total capital reserve: $6,975 per year, or approximately 8.8 percent of gross rent.

Combined vacancy and reserves: 18.3 percent of gross rent, not the 10 percent most proformas show. That single correction changes your NOI by $6,600 annually on this property.

Debt Service Coverage Ratio: What It Means and How to Calculate It

Debt Service Coverage Ratio, or DSCR, is the ratio of Net Operating Income to annual debt service. Lenders require it because they want to confirm the property itself generates enough income to cover loan payments with a cushion.

Formula: DSCR = NOI divided by Annual Debt Service.

Using our example: $39,892 divided by $64,476 = 0.62.

Most conventional lenders require a DSCR of 1.20 or higher. DSCR loans, which underwrite based purely on property income rather than borrower income, typically require 1.25. Our property at 0.62 fails DSCR underwriting entirely on a 25 percent down payment at current rates.

To reach a 1.20 DSCR, the NOI must equal 1.20 times the debt service. At $64,476 annual debt service, the required NOI is $77,371. This property generates $39,892. The gap is $37,479 annually. Bridging that gap requires either dramatically higher rents, a much larger down payment to reduce debt service, or a substantially lower purchase price.

If you put 40 percent down instead of 25 percent, the loan amount drops to $630,000, annual debt service drops to $51,581, and DSCR improves to $39,892 divided by $51,581 = 0.77. Still below threshold. The math on Boston multi-family at current prices does not clear institutional DSCR requirements at realistic rent levels, which is why many Boston investors use portfolio lenders and local credit unions rather than agency financing.

How Lenders Evaluate Multi-Family Loans Differently Than Single Family

On a single family purchase, lenders focus almost entirely on your personal income, credit score, and debt to income ratio. The property’s rent potential is largely irrelevant since you are expected to pay the mortgage from your job income.

On a two to four unit property that you owner-occupy, lenders will credit 75 percent of projected rental income from the non-owner-occupied units toward your qualifying income. On a three family where you occupy one unit, two units at $2,200 each generate $4,400 gross. Seventy-five percent = $3,300 per month added to your qualifying income. This is called the “self-sufficiency” calculation and it meaningfully improves how your application looks.

On a non-owner-occupied two to four unit investment property, lenders use Schedule E income from existing tax returns to qualify you, not the leases. If you already own rentals and show losses on your Schedule E (which is extremely common due to depreciation), those paper losses count against your qualifying income even though they do not represent real cash outflows. This surprises many investors the first time they refinance or try to buy a second property.

Checking your credit profile before applying is essential since investment property loans typically require a 680 minimum score and the rate tiers improve significantly at 720 and 740. A service like SmartCredit lets you monitor your score and dispute any errors before a lender pulls your credit, which can save you hundreds of dollars monthly in rate differences on a large loan.

The Breakeven Rent Calculation for Massachusetts Properties

Breakeven rent is the minimum rent you must collect to cover all expenses including debt service without losing money. It is the floor below which the property destroys value.

Formula: Breakeven Rent = (Total Operating Expenses plus Annual Debt Service) divided by (1 minus Vacancy Rate) divided by 12 divided by Number of Units.

For our triple decker: Total operating expenses $34,556 plus debt service $64,476 = $99,032. Divide by (1 minus 0.06 vacancy) = $99,032 divided by 0.94 = $105,353. Divide by 12 = $8,779 per month total. Divide by 3 units = $2,926 per unit per month.

Market rent is $2,200. Breakeven requires $2,926. The property needs rents to grow 33 percent before it breaks even at current financing costs.

Massachusetts specific costs that inflate breakeven significantly compared to Sun Belt properties include mandatory snow removal liability (you can be sued if a tenant or visitor falls and sidewalks are not cleared, making snow removal a non-negotiable budget line), above average heating oil and natural gas costs, the highest water and sewer rates in New England in Boston proper, and the requirement to maintain landlord-side heating in most multi-family configurations under Massachusetts General Law Chapter 186. These are not optional cost categories.

Comparing 2 Family vs 3 Family vs 4 Family Investment Math Side by Side

The property type changes your math in ways that go beyond simply multiplying by more units.

Two Family at $750,000 in JP, Rents at $2,400 Each

Gross annual rent: $57,600. Vacancy at 6 percent: $3,456. Effective gross: $54,144. Operating expenses (proportionally lower per unit): $22,800. NOI: $31,344. At 25 percent down, loan of $562,500 at 7.25 percent, debt service: $46,001. Annual cash flow: negative $14,657. Cap rate: 4.18 percent. DSCR: 0.68.

Three Family at $1,050,000 in Dorchester, Rents at $2,200 Each

As fully calculated above. NOI: $39,892. Cap rate: 3.80 percent. DSCR: 0.62. Annual cash flow: negative $24,584.

Four Family at $1,350,000 in Roslindale, Rents at $2,100 Each

Gross annual rent: $100,800. Vacancy at 6 percent: $6,048. Effective gross: $94,752. Operating expenses (four units, older building): $44,200. NOI: $50,552. At 25 percent down, loan of $1,012,500 at 7.25 percent, debt service: $82,801. Annual cash flow: negative $32,249. Cap rate: 3.74 percent. DSCR: 0.61.

The four family actually has the worst DSCR of the three even though it generates more NOI, because the debt load scales faster than the income. The two family produces the best cap rate and the least negative cash flow in dollar terms. However, the two family has less diversification risk since losing one tenant means losing 50 percent of your income rather than 25 to 33 percent. The three family remains the most common investor choice in Greater Boston for reasons that are partly mathematical and partly practical.

Common Math Mistakes That Overstate Returns

These errors appear on virtually every optimistic proforma a seller’s broker presents to you.

Using gross rent instead of net rent in the cap rate numerator overstates NOI by 20 to 30 percent before you even account for expenses. The only correct NOI starts with effective gross income after vacancy.

Using asking rents rather than actual signed lease amounts inflates income. Always verify rent rolls and ask for actual lease documents. On a Boston triple decker, an owner-occupied unit is often listed at market rent on the proforma even though no one is actually paying that amount.

Excluding property management because you plan to self-manage is a mistake even if you intend to manage the property yourself. You are providing labor with real economic value and a property that only works if you work for free is not truly profitable. Include management at 8 to 10 percent regardless.

Ignoring capital expenditure reserves because the building “was recently renovated” misunderstands how building systems work. A new kitchen does not extend the life of a 30 year old boiler or a 15 year old roof. Each system depreciates independently. Reserve for all of them.

Applying national vacancy rates of 3 to 5 percent to a building with long-term below-market tenants ignores the near-certain vacancy cliff when those tenants eventually leave and units need to be brought to market. Always model at least one turnover per unit in a rolling 18-month period.

Forgetting Massachusetts transfer taxes, attorney fees, and the cost of a proper