THE NUMORIX GUIDE
How to use the Rental Property Calculator
Last reviewed September 14, 2026
What this calculator does
The analysis forms loan amount from purchase price minus down payment when useLoan is true, then calculates monthly mortgage.
Formula and method
The analysis forms loan amount from purchase price minus down payment when useLoan is true, then calculates monthly mortgage. Each year it grows rent and expenses, subtracts vacancy and management fees from gross rent, subtracts operating expenses and mortgage from net income, and grows property value by appreciation. It combines cumulative cash flow and sale proceeds after cost to sell and an estimated remaining balance to produce total profit.
Variables and inputs
Inputs cover purchase price, loan choice, down payment, rate, term, closing cost, repairs, operating expenses and their growth, rent and other income, vacancy, management fee and rent growth, appreciation, holding years, and cost to sell. Dollar fields are currency; rates are annual percentages; holding length is years.
Worked example
With $350,000 purchase price, $70,000 down, $2,200 monthly rent, 8% vacancy, 10% management, $4,200 tax, $1,800 insurance, and $3,500 maintenance, year-one gross rent is 2,200 x 12 = $26,400. Vacancy is $2,112 and management is $2,640, so gross income after those deductions is $21,648; operating expenses are 4,200 + 1,800 + 3,500 = $9,500, leaving $12,148 before mortgage.
How to interpret the result
Cash flow is the money left after modeled operating costs and mortgage, while cap rate and cash-on-cash use different denominators. Total profit also includes modeled appreciation and sale proceeds. Negative year-one cash flow does not by itself make a property unviable, but it must be funded.
Common mistakes to avoid
Separate vacancy from management percentage. Include closing costs and repairs in total investment. Do not treat gross rent as usable cash before taxes, insurance, maintenance, financing, vacancy, and management are deducted.
Assumptions and limitations
The mortgage-balance estimate is simplified and the sellPrice and valueAfterRepairs fields are not used in the final calculation. The model excludes depreciation, income tax, financing fees, capital expenditures beyond entered maintenance, rent collection risk, legal costs, and local landlord rules.