How to Estimate Rental Property Cash Flow

The arithmetic of rental property cash flow takes about four minutes. The estimate is what goes wrong, and it goes wrong in the same three places almost every time: rent that is scheduled rather than collected, expenses that have not happened yet, and a loan payment nobody has actually quoted.

Cash flow is what is left after the property has paid for itself, including the loan. Everything below is how to get to that number honestly, and what a lender does with it once you bring it in. If you are earlier than that and still deciding whether to buy at all, start with buying your first Minnesota rental.

What cash flow is, in one line

Rental property cash flow is effective rental income minus operating expenses minus debt service, measured over a full year.

Two words in that sentence do most of the work. Effective means income you expect to actually collect, not the rent roll on the listing. Full year means twelve months including the vacant one, the furnace, and the January when nobody moves.

Estimate it in five steps

Step 1. Start with scheduled rent, not hoped-for rent

Add up every income stream the property produces in a year: rent on each unit, garage or parking, coin laundry, storage, pet rent. Use what comparable units in that neighborhood are renting for today, not what the seller says the units could get after improvements. Our post on rental comps covers how to pull that yourself.

A pro forma supplied by a seller is a sales document. It is a fine place to start and a poor place to finish.

Step 2. Take vacancy out before anything else

A vacancy allowance is not pessimism, it is arithmetic. One month empty on a twelve month lease is 8.3 percent of that unit's annual income, and turnover costs paint and cleaning on top of the lost rent. Five percent is a common starting assumption on a stabilized property in a steady market. Adjust it up for student housing, short term rentals, or a building that has turned over three times in two years.

Scheduled income minus vacancy is your effective gross income. Every percentage below runs off that number, not off the rent roll. Good tenant screening is the cheapest vacancy control there is, because the expensive vacancies are the ones that follow an eviction.

Step 3. List operating expenses, including the ones that have not happened yet

Operating expenses are everything the property costs to run, before the mortgage. The line items owners get right are taxes and insurance. The ones they miss are the ones that have not billed yet:

• Capital reserve. Roofs, furnaces, water heaters, and parking lots all have a replacement date. Setting aside money monthly is what turns a $9,000 furnace into a budget line instead of an emergency.
• Property management. Put it in the estimate even if you plan to self manage. If you do the work you pay yourself, and if your situation changes you have already priced the replacement. Eight to ten percent of collected rent is a common range.
• Snow and lawn. In Minnesota this is a twelve month expense with two different vendors, and on a small multifamily it is rarely optional.
• Owner paid utilities. Water, sewer, and trash are frequently the owner's on a duplex or fourplex even when heat is not.
• Turnover. Paint, cleaning, locks, and listing costs, every time a unit changes hands.

Leave out anything that is not an operating cost of the building: your mortgage principal and interest, income taxes, depreciation, and the capital improvement itself when you replace the roof. Those belong elsewhere in the analysis.

Step 4. Subtract debt service

Debt service is the actual annual principal and interest payment on the loan you will actually have. Not the rate. The payment.

This is the step most estimates hand wave, and it is the one with the widest range of outcomes, because the same loan amount at the same rate produces a materially different payment depending on how long it is amortized over. More on that below.

Step 5. Read the answer three ways

One number is not enough to judge a deal.

• Monthly cash flow tells you whether the property pays you or you pay it.
• Cash on cash return is annual cash flow divided by the cash you actually put in, including down payment, closing costs, and initial repairs. It is the number that lets you compare a duplex against anything else you could do with the same money.
• Debt service coverage is net operating income divided by annual debt service. It is how your lender will read the same property, and it is usually what sets the maximum loan rather than the purchase price.

Net operating income, cap rate, and the rest of the vocabulary a lender will use are laid out in our guide to investment real estate financing.

A worked example: a Waconia duplex

Numbers are illustrative. They are not a rate quote, an appraisal, or an offer of credit, and they are not market data for any specific address. The point is the shape of the arithmetic.

A duplex at a $285,000 purchase price. Two units at $1,450 a month, plus $50 a month for a garage stall. Twenty five percent down, so a $213,750 loan.

That is $37 a month. On roughly $80,000 of cash in the deal once closing costs and initial repairs are counted, it is a cash on cash return of about half a percent.

Notice what just happened. This property passes the 1 percent rule. It rents for $2,950 against a $285,000 price, which clears the $2,850 the rule asks for. It still produces $37 a month, and its debt service coverage is 1.02, which is under the cushion most lenders look for. The rule said yes and the arithmetic said barely.

The $1,511 monthly payment is what $213,750 costs at a twenty five year amortization and a 7 percent rate. Your payment will be different. Ask a lender for a payment, not a rate, because the payment is the number cash flow actually reacts to.

Bringing a filled in version of this table to a first conversation changes the meeting. If you want help pulling the numbers together on a specific property, talk with a business lender before you write the offer rather than after.

How financing changes the answer

This is the part of cash flow that gets the least attention and moves the number the most.

Amortization is a bigger lever than most owners expect

Take the same $213,750 loan at the same 7 percent and amortize it over twenty years instead of twenty five. The payment goes from $1,511 to $1,657. Annual debt service goes from $18,132 to $19,884, and the property that produced $448 a year now loses $1,304. Coverage falls from 1.02 to 0.93.

Nothing about the building changed. Same rent, same taxes, same roof. A five year difference in amortization was the whole result. We amortize investment real estate up to twenty five years depending on loan to value, which is one of the structural questions worth raising in the first conversation rather than the last.

Your term and your amortization are two different numbers

On commercial and investment real estate the loan is commonly written with a rate fixed for three, five, or seven years and a payment amortized over a longer schedule. The amortization sets today's payment. The term sets the date your rate is revisited.

An estimate built on today's payment is an estimate of today. Run the same table at a higher payment and see whether the property still works, because that is the question you will face at the reset, and it is a better time to answer it than the week the notice arrives. How the whole structure fits together is on our commercial real estate loans in Minnesota page.

The lender is running your arithmetic back at you

Debt service coverage is the same calculation from the other side of the table. Net operating income divided by annual debt service. A property with $120,000 of net operating income and a $100,000 annual payment covers at 1.20. Lenders look for a cushion above 1.00 so the property carries its own debt with room for a vacancy and a repair, and coverage rather than purchase price is usually what sets the maximum loan.

The practical consequence is that your expense assumptions are not private. If you left the capital reserve out and we put it back in, your coverage drops and so does the loan. The worked example above is the version worth building yourself, because it is the version that survives underwriting. Our post on debt service coverage ratio walks through the math with examples.

Refinancing moves cash flow in both directions

A refinance can lower a payment, extend an amortization, or pull equity out for the next purchase. It can also reset a rate upward and take cash flow with it. Either way it is a cash flow event before it is anything else, and the table above is how you find out which one it is. Our guide to commercial loan refinancing covers what to weigh, including prepayment penalties that can outrun the savings.

One more constraint worth knowing before the portfolio grows: conventional financing caps how many rental properties one borrower can finance, separately from how much any single property can carry. We covered both in financing limits on 1 to 4 family rentals in Minnesota.

What the 1 percent rule and the 50 percent rule are good for

Both rules are screens, not answers. They exist so you can rule a listing out in ten seconds without building a spreadsheet.

The 1 percent rule says monthly rent should be at least 1 percent of the purchase price. On a $285,000 property that is $2,850 a month. It is a rent to price test and it says nothing about taxes, insurance, or what the loan costs, which is why the example above passed it and still returned $37 a month.

The 50 percent rule estimates that operating expenses will consume about half of rental income, excluding the mortgage. In the example, expenses ran $15,050 against $35,400 of scheduled rent, or roughly 43 percent, so the rule was conservative in that direction. It is a useful sanity check when you suspect an expense list is too short.

Neither rule was designed for the payment environment you are borrowing in today, and no lender underwrites to either one. Use them to sort a list. Use the five steps to decide.

Five ways to actually move the number

• Raise rent to market, on schedule. A unit that has drifted 8 percent under market for three years is the largest and least expensive fix available. Our post on when to raise rent covers the timing and the conversation.
• Cut turnover, not maintenance. Deferring repairs raises turnover, and turnover costs more than the repair did. Retention is a cash flow strategy.
• Add income that does not add a tenant. Garage stalls, storage, and laundry carry almost no incremental expense, so nearly all of it lands in net operating income.
• Reprice the recurring bills. Insurance, lawn and snow, and management contracts are all renewable and rarely renegotiated. Energy efficiency work belongs here too when the owner pays the utility.
• Restructure the debt. The amortization comparison above moved cash flow by $1,752 a year on a single property, which is more than most operational changes will produce.

Changing the use is a different decision rather than an optimization. Short term rental financing works differently and the income is seasonal, so the vacancy assumption changes with it.

Where estimates go wrong

• Using gross rent instead of effective income. Skipping vacancy overstates every downstream number.
• No capital reserve. The most common single omission, and the one that turns a positive year into a negative one on the day the furnace quits.
• Self managing for free. Free until you get busy, move, or the building grows.
• Averaging a repair budget off one quiet year. Older buildings have quiet years. They do not have quiet decades.
• Estimating the payment from a rate you saw online. Get a payment quoted on the actual loan amount, amortization, and structure. It is also the first thing a lender builds when underwriting income property.

Frequently asked questions

What is cash flow in real estate?

Cash flow is the money left over after a property has paid its own operating expenses and its loan payment for the period. Positive cash flow means the property produces more than it costs to own and operate. Negative cash flow means the owner covers the difference out of pocket.

How do you calculate cash flow on a rental property?

Add all income the property collects in a year, subtract a vacancy allowance to get effective gross income, subtract operating expenses to get net operating income, then subtract annual debt service. What remains is annual cash flow. Divide by twelve for the monthly figure.

What is a positive cash flow property?

A property whose collected income exceeds its operating expenses and loan payments over a full year, so it distributes cash to the owner rather than requiring contributions. A property can be positive on a monthly basis and negative annually once a vacancy and a large repair are included, which is why the measurement period matters.

What is good cash flow on a rental property?

There is no universal dollar figure, because the right answer depends on how much cash is invested and what else that cash could do. Two benchmarks are more useful than a target dollar amount: cash on cash return, which compares the cash flow to the money you put in, and debt service coverage, where a ratio of 1.20 or higher is a common benchmark in commercial real estate lending. Your lender will discuss the target that fits your property type.

How does real estate financing impact cash flow?

Financing sets the largest single line in the calculation, and it sets it through the payment rather than the rate alone. Loan amount, amortization period, and rate together determine debt service. Lengthening amortization lowers the payment and raises cash flow while increasing total interest paid. Shortening it does the reverse. A five year change in amortization on a mid six figure loan can move annual cash flow by more than most operational improvements will.

What expenses should be included in a rental property cash flow estimate?

Property taxes, insurance, owner paid utilities, repairs and maintenance, a capital reserve, property management, landscaping and snow removal, turnover costs, and any association dues. Exclude income taxes, depreciation, and the mortgage from the operating expense list. The mortgage is subtracted separately as debt service, and depreciation is a tax item rather than a cash item.

Should the mortgage payment be included in cash flow?

Yes, but at the right step. Net operating income is calculated before the mortgage, because that is the number a lender and an appraiser use to value the property independent of how any one buyer finances it. Cash flow is calculated after the mortgage. Both are useful and they are not interchangeable.

What is the difference between cash flow and net operating income?

Net operating income is income after operating expenses but before debt service. Cash flow is what is left after debt service as well. Two buyers looking at the same building will compute the same net operating income and different cash flow, because they will finance it differently. That separation is why net operating income is the figure used in valuation and in investment real estate financing.

What is before tax cash flow?

Before tax cash flow is net operating income minus debt service, without adjusting for income taxes, depreciation, or the tax treatment of interest. It is the standard figure quoted in a rental analysis and it is what the worked example above produces.

How do you estimate cash flow on a commercial property?

The method is the same, with two differences in the inputs. Leases carry their own expense structure, so who pays taxes, insurance, and maintenance is set by the lease type rather than by convention. Vacancy is measured against lease expiration dates rather than a flat percentage, because a single expiring tenant can move the number more than a year of turnover on a duplex. Our post on what drives commercial real estate value covers how those inputs feed valuation.

Does the 1 percent rule still work?

As a screen, yes. As a decision, no. It compares rent to purchase price and ignores taxes, insurance, and the cost of the loan, all three of which have moved considerably since the rule became popular. The worked example above passes it and still produces $37 a month.

How much cash flow do I need to qualify for an investment property loan?

Qualification is expressed as coverage rather than as a dollar figure. Lenders divide net operating income by annual debt service and look for a cushion above 1.00, and that ratio commonly sets the loan amount before the purchase price does. Property type, condition, loan to value, and the financial strength of the guarantors all factor in, which is why the answer comes out of a conversation about a specific property rather than a table.

Talk it through before you write the offer

The estimate above is worth more before an offer than after one. It is also the fastest way to get a realistic answer from a lender, because it puts the two numbers we look at first, net operating income and debt service, on one page.

Security Bank & Trust Co. has lent against Minnesota real estate since 1935, and the person who reads your deal works here. We are recognized among Minnesota's top banks, with 21 locations across 18 Minnesota communities from Glencoe and Winsted to Waconia, Chaska, Cambridge and Wayzata. Bring the table, filled in with your own numbers, and talk with a business lender.

This article is general information about how rental property cash flow is calculated. It is not financial, tax, or legal advice, and the figures in the worked example are illustrative rather than a quote, an appraisal, or an offer of credit. Talk with your own tax advisor about your situation. Page last reviewed August 2026.