Deal Analysis
Rental Income Calculator: How to Project Rental Cash Flow
The four numbers between the rent on a listing and the cash you keep, the assumptions behind each, and a worked example you can copy.
A rental income calculator answers one question in four steps: of the rent a property collects, how much do you keep? The steps are the same on a spreadsheet, a free online calculator or a full analysis, and the answer is only as good as the assumptions on each line. This guide walks the waterfall from gross rent to cash flow, gives working ranges for every assumption, and works a complete example.
What a rental income calculator calculates
The calculator takes a rent figure and a handful of expense assumptions and produces four numbers, each one net of something the one before it ignored. Investors who skip a step are usually the ones surprised by the cash flow after closing.
| Number | Formula | What it tells you |
|---|---|---|
| Gross rental income | Monthly rent × 12 | The most the property can collect at full occupancy |
| Effective gross income | Gross income − vacancy allowance | What it collects in a normal year with turnover |
| Net operating income (NOI) | Effective gross income − operating expenses | The property's profit before financing; the base for cap rate and DSCR |
| Cash flow | NOI − annual mortgage payments | What lands in your account; the base for cash-on-cash return |
Two of those figures matter to a lender and two matter to you. Net operating income is what an appraiser and a DSCR lender look at; cash flow is what pays for the next property.
The income waterfall, line by line
Gross rental income = Monthly rent × 12
Use the rent the comparables support, not the listing agent's projection. The rent estimate is the whole calculation's foundation.
Effective gross income = Gross income × (1 − vacancy rate)
A 5% allowance is 18 days empty a year. Turnover, a week of cleaning and a week of showings use that up on their own.
NOI = Effective gross income − operating expenses
Taxes, insurance, maintenance, capital reserves, management, HOA dues and any owner-paid utilities. Never the mortgage.
Cash flow = NOI − annual debt service
Principal and interest for the year. Divide by 12 for the monthly figure most investors quote.
The order matters. Vacancy comes off the top because you cannot pay management on rent you did not collect, and management is usually a percentage of collected rent. Reserves come off before the mortgage because the roof does not wait for the loan to be paid down.
The expense assumptions that decide the answer
Most rental income calculations go wrong on the expense side, not the rent side. Two lines, taxes and insurance, should be actual figures; the rest are percentages with defensible ranges.
| Expense | Typical range | How to get the real figure |
|---|---|---|
| Property taxes | 1% to 2.5% of value a year | County assessor; assume reassessment to your purchase price |
| Insurance | $1,000 to $2,500 a year, far more in coastal states | An actual quote before the offer, with wind and flood where required |
| Vacancy | 5% to 10% of gross rent | Local property managers; days on market for nearby listings |
| Maintenance and repairs | 5% to 10% of rent | Higher for older homes; inspection report for known items |
| Capital expenditure reserve | 5% of rent, more on older systems | Age of roof, HVAC, water heater and appliances |
| Property management | 8% to 10% of collected rent | Quotes from two managers; include the leasing fee |
| HOA dues | Actual | The association's current statement and any special assessments |
Added together, operating expenses on a typical single-family rental run 35% to 45% of gross rent before the mortgage. A calculation showing 20% has lines missing.
A worked example: from $2,500 in rent to cash flow
A 3-bed, 2-bath single-family home listed at $260,000, with rent supported at $2,500 a month by five comparables. Financing is 20% down with a $208,000 loan at 7% over 30 years, which costs $1,384 a month in principal and interest.
Step 1: Net operating income for the year
- Gross rental income$2,500 × 12
- $30,000
- Vacancy allowance (5%)
- −$1,500
- Effective gross income
- $28,500
- Property taxes1.15% of the purchase price
- −$3,000
- Insurance
- −$1,200
- Property management (10% of collected rent)
- −$2,850
- Maintenance (5% of gross rent)
- −$1,500
- Capital reserve (5% of gross rent)
- −$1,500
- HOA dues
- −$600
- Net operating incomeOperating expenses of $10,650 are 35.5% of gross rent
- $17,850
Step 2: Cash flow after the mortgage
- Net operating income
- $17,850
- Annual debt service$1,384 × 12
- −$16,608
- Annual cash flow$104 a month
- +$1,242
That result is the typical 2026 outcome for a rent-to-price ratio under 1%: sound operating income, thin cash flow once the loan is included. The useful move is not to revisit the rent estimate but to ask what price makes the numbers work, which is what a cash-on-cash target or a maximum offer calculation answers.
Example uses public listing data for illustration. See disclaimer.
Reading the result: which number to act on
Four outputs come out of the calculation and each answers a different question. Compare them against the targets below before you decide anything, and notice which one is the binding constraint.
| Output | Built from | Working target | In the example |
|---|---|---|---|
| Monthly cash flow | NOI − mortgage | $150 to $200 or more per unit | $104 |
| Cash-on-cash return | Annual cash flow ÷ cash invested | 8% or higher | 2.2% |
| Cap rate | NOI ÷ price | 5% to 8%, market dependent | 6.9% |
| DSCR | NOI ÷ annual debt service | 1.20 to 1.25 or higher for most lenders | 1.07 |
In the example the binding constraints are cash-on-cash and DSCR, and both move with the same two inputs: purchase price and loan size. A price of roughly $235,000, or the same price with 30% down, brings DSCR above 1.2. The rent, the expenses and the property itself did not need to change.
Projecting rental income beyond year one
A single-year calculation is a snapshot. Rent, expenses and the loan balance all move, and a multi-year projection shows whether thin year-one cash flow becomes comfortable by year five or stays thin because expenses grow as fast as rent.
Use modest assumptions: 2% to 3% annual rent growth, 3% expense growth, and a flat mortgage payment. On the example above, 3% rent growth adds about $900 of gross rent in year two while the mortgage stays at $16,608, so cash flow improves each year even before any appreciation.
Example uses public listing data for illustration. See disclaimer.
Mistakes that make a rental income calculation lie
- Asking rent instead of achievable rent. Listings lease 3% to 8% below asking, more when they sit. Use comparables and lease data, not the agent's figure.
- The seller's numbers. A seller's pro forma exists to sell. Rebuild every line from your own sources.
- Zero vacancy. Every property turns over. 5% is the floor.
- Last year's tax bill. Most counties reassess at sale. Estimate taxes on your purchase price, not the seller's basis.
- Comparable rents from renovated units. If the comps are updated and the subject needs work, the subject does not get their rent until the work is done.
Frequently asked questions
What is the difference between gross rental income and net rental income?
Gross rental income is the rent at full occupancy, monthly rent times twelve. Net rental income, usually called net operating income, is what is left after vacancy and every operating expense: taxes, insurance, maintenance, management, reserves and HOA dues. The mortgage comes off after that to give cash flow.
What vacancy rate should a rental income calculator use?
5% for a typical single-family rental in a stable market, which is about 18 days empty a year. Use 8% to 10% for high-turnover markets, small units or student rentals, and 3% to 5% only where long-term tenants and fast lease-ups are documented. Never 0%.
Is rental income calculated before or after the mortgage?
Both, at different steps. Net operating income is before the mortgage and is what cap rate and DSCR are built on. Cash flow is after the mortgage and is what you actually keep. A calculator that stops at either one is showing you half the picture.
How much should I budget for maintenance and capital expenses?
Around 5% to 10% of rent for maintenance and another 5% for capital reserves on a typical single-family home, more on older properties. Roofs, HVAC and water heaters arrive on a schedule whether or not you saved for them, so a calculator that omits reserves overstates income.
Why does my rental income calculation show negative cash flow?
At 2026 mortgage rates, a property whose rent is under about 1% of its price often produces positive net operating income and negative cash flow once the loan payment is included. The fix is a lower price, a larger down payment, or a different property, not a more optimistic rent figure.
Keep reading
How to Estimate Rent for an Investment Property
The first line of the waterfall, and how to get it right.
Read articleHow to Calculate Cash-on-Cash Return
What the cash flow figure is worth relative to the cash you put in.
Read articleCap Rate Calculator: Real Estate Investment Analysis
The metric built directly on net operating income.
Read articleDSCR Explained
The lender's test that runs on the same two numbers.
Read articleRun the full waterfall on a real address
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