This real estate calculator builds a simple monthly investment snapshot. It finances price minus down payment at the mortgage rate and term, then subtracts that payment and monthly expenses from expected rent. The default case (350000 price, 70000 down, 6.5% for 30 years, rent 2200, expenses 400) lands near 30.21 in monthly cash flow.
Use it to sanity check whether rent covers debt service and operating costs before deeper underwriting. For payment only math, try the mortgage calculator or the loan calculator.
How the formula works
Loan = max(0, price – down). Compute the amortizing monthly payment for that loan. Cash flow = rent – expenses – payment.
Worked example
Loan = 280000. Payment is about 1769.79. Rent 2200 minus expenses 400 minus payment leaves about 30.21.
| Input | Value |
|---|---|
| Property price | 350000 |
| Down payment | 70000 |
| Rate / term | 6.5% / 30 years |
| Rent / expenses | 2200 / 400 |
| Monthly cash flow | about 30.21 |
How to use the fields
- Property price is the purchase price.
- Down payment reduces the financed amount.
- Mortgage rate and term set the amortizing payment.
- Expected monthly rent and monthly expenses complete the cash flow.
Thin margins
The default is barely positive. Small expense increases or rent cuts flip the sign. That sensitivity is useful: it shows how fragile a deal can look before vacancy, repairs, and capex.
Common mistakes
- Leaving taxes, insurance, or HOA out of expenses
- Using optimistic rent with no vacancy haircut
- Comparing cash flow without matching down payment assumptions
- Reading cash flow as equity ROI
Stress tests
Raise expenses by a fixed amount and rerun. Lower rent slightly and rerun. If both cases go negative quickly, the deal needs a stronger rent thesis or a larger down payment.
Financing notes
The payment model is a standard amortizing loan. Interest only periods, balloons, points, and PMI are not modeled. Adjust the rate or loan size yourself if you need a rough proxy.
Planning workflow
Lock price and down payment first, confirm the payment, then layer rent and expenses. Changing every input at once hides which lever hurt cash flow.
Write the payment and cash flow side by side so partners see both debt service and leftover dollars.
Down payment effect
Larger down payments shrink the loan and the monthly payment, which lifts cash flow if rent and expenses stay fixed. The tradeoff is more cash tied up at purchase.
Run the default, then raise down payment by a round amount and note both cash flow and cash required so partners see the full picture.
Expense realism
Maintenance, vacancy adjacent costs, and management fees often hide in the expenses line. Underestimating expenses is the fastest way to invent positive cash flow on paper.
If you are unsure, start with a higher expense assumption and see whether the deal still clears a small positive number.
Rent support
Comparable rents should back the rent field. A marketing flyer rent that the market will not pay creates a false snapshot. Keep comps beside the calculator inputs.
When rent barely covers payment and expenses, as in the default, treat the deal as fragile until reserves and vacancy planning are explicit.
Cap rate is different
Cap rate styles divide net operating income by price and ignore financing. This calculator includes financing in the cash flow snapshot, so it answers a different question.
Use cash flow when debt service matters to your plan. Use a separate cap style metric when you want an unlevered view.
Do not mix the two numbers in one sentence without saying which definition you mean. Partners make bad calls when cash flow and cap rate language blur together.
If expenses already net some items from rent, do not double count them in the expenses field.
Limitations
No appreciation, no tax shelter, no rehab budget, and no vacancy schedule. Treat the output as a first pass monthly snapshot only.