Rental Property Cash Flow Calculator

How rental cash flow works

Rental cash flow is simply what's left over every month after every real cost of owning the property has been paid. In its most basic form, the formula is: cash flow = rental income − mortgage payment − operating expenses − reserves. The tricky part isn't the subtraction — it's remembering to include every cost that actually shows up over a full year of ownership, not just the ones that hit your bank account this month.

Most new investors start with a version of this formula that only accounts for rent and mortgage. That version looks great on paper because it ignores everything that isn't a fixed monthly bill: vacancy between tenants, a water heater that fails in year four, a management company's cut, or the week a unit sits empty during a turnover. This calculator builds those costs in as monthly reserves, so the number you see is closer to what you'll actually experience over time, not just what happens in a lucky month with no surprises.

It also matters whether you're looking at gross cash flow or net cash flow. Gross cash flow usually means rent minus the mortgage payment alone. Net cash flow subtracts everything: the mortgage, property management, maintenance and capital expenditure reserves, vacancy, insurance, HOA dues, and any other recurring cost. Listing pro formas may leave out some costs, so always check which expenses a quoted number includes. Net cash flow is the number that determines whether a property genuinely puts money in your pocket, so it's the one this tool is built around.

What each input means and why it matters

Every field in the calculator above represents a real category of income or cost that a rental property generates. Here's what each one is doing in the math, and why skipping it produces a misleading result:

• Monthly rental income. This should be the rent you actually expect to collect, not an optimistic asking price you've never tested against the local market. If you're evaluating a property you don't yet own, use comparable active listings and recently leased units nearby, not the landlord's stated rent history alone.
• Monthly mortgage payment (PITI). PITI stands for principal, interest, taxes, and insurance — the full monthly housing payment, not just the loan's principal-and-interest portion. If you enter a principal-and-interest-only figure here, your final cash flow number will be overstated because taxes and insurance are already real, unavoidable monthly costs.
• Property management (%). Even if you plan to self-manage today, budgeting a management percentage protects you if your circumstances change, and it gives you an apples-to-apples number to compare against a property you might eventually hand off to a manager. Typical third-party management fees run in the high single digits to low double digits of collected rent, though this varies by market and service level.
• Maintenance reserve (%). Roofs, water heaters, HVAC systems, and appliances don't fail on a predictable monthly schedule — they fail all at once, usually at an inconvenient time. Setting aside a percentage of rent every month, whether you spend it that month or not, is how experienced landlords avoid being caught without cash when something breaks.
• Vacancy reserve (%). No rental stays occupied 100% of the time forever. Turnover between tenants, an eviction, or a slow rental season can all mean a month or more of lost rent. Reserving for vacancy even during months the unit is fully occupied smooths out the inevitable gap instead of letting it wreck a single month's numbers.
• Other monthly expenses. HOA dues, landlord insurance if it isn't already folded into your PITI figure, pest control contracts, lawn care, or utilities you cover as the owner all belong here. These are easy to forget because they're often billed separately from the mortgage, but they reduce your cash flow just the same.

A worked example

Here's an illustrative example using round numbers, not a real listing. Say you're considering a single-family rental with a monthly rent of $2,200 and a mortgage payment (PITI) of $1,300. You budget 8% of rent for management ($176), 5% for maintenance ($110), and 5% for vacancy ($110), plus $100 a month for miscellaneous costs like landlord insurance and lawn service.

Add those up: $1,300 + $176 + $110 + $110 + $100 = $1,796 in total monthly outflow. Subtract that from $2,200 in rent, and you're left with roughly $404 in estimated monthly cash flow. That's the number that matters for deciding whether the deal is worth pursuing — not the $900 a month you'd get by only subtracting the mortgage payment from rent and ignoring reserves. The gap between those two numbers is exactly why so many new landlords are surprised by their first major repair bill or vacancy stretch.

Common mistakes when estimating cash flow

• Using gross rent instead of realistic, market-tested rent. A rent estimate pulled from a listing agent's pitch or a seller's pro forma is often higher than what the unit will actually command once it's on the open market.
• Forgetting vacancy and maintenance reserves entirely. A property that "cash flows" only when it's occupied every single month and nothing ever breaks isn't a property that actually cash flows — it's a property that hasn't hit a bad month yet.
• Confusing principal-and-interest with full PITI. Leaving taxes and insurance out of the mortgage line item is one of the most common ways beginners overstate how much a property will actually net them.
• Ignoring capital expenditures. Routine maintenance covers small repairs; it doesn't cover a full roof replacement or a new HVAC system. Some investors track a separate CapEx reserve on top of a maintenance reserve for exactly this reason.
• Treating the first year's numbers as permanent. Property taxes get reassessed, insurance premiums rise, and rent needs to keep pace with the local market. A property that cash flows today can tighten up within a few years if none of those numbers are ever revisited.

Limitations of this calculator

This tool estimates monthly operating cash flow from the inputs you provide. It does not calculate appreciation, tax depreciation benefits, loan amortization or principal paydown over time, closing costs, or the total return on your invested cash (cash-on-cash return). It also can't know your local market's actual vacancy rates, insurance costs, or property tax assessment practices — those numbers are only as accurate as what you enter. Treat every result as a starting estimate to sanity-check a deal, not a final underwriting number, and verify your specific mortgage, tax, and insurance figures directly with your lender, county assessor, and insurance carrier before making a purchase decision.

Keep learning