Unlike a bare cash-flow model, this calculator has dedicated fields for maintenance and property management, each entered as a percentage you set — maintenance against gross rent, management against effective (post-vacancy) rent. At the national median price and rent, financed at 6.71%, illustrative 5% maintenance and 8% management inputs alone turn a roughly break-even deal into monthly cash flow of about −$436, which is the whole point of running your own percentages rather than skipping the fields.
How this calculator's expense model differs
This module amortizes a standard 30-year mortgage from purchase price and down payment, then builds expenses in a specific order: monthly effective rent = gross rent × (1 − vacancy rate), maintenance cost = gross rent × maintenance %, and management cost = effective rent × management %. The base each percentage applies to is not the same — maintenance is a percentage of what the unit could earn if fully occupied, management a percentage of what it actually collects after vacancy. That distinction matters because it means maintenance cost does not fall when vacancy rises, while management cost does, which is realistic: a property manager who does not collect rent for a vacant month does not usually earn a fee on it, but the roof still needs the same maintenance budget whether or not the unit is occupied.
Neither percentage is a rule this calculator asserts as correct — they are fields you set. This page does not default to a specific maintenance or management percentage, and no verified national average for either exists in the sources behind this page. The worked example below uses illustrative round figures (5% and 8%) purely to demonstrate the arithmetic; substitute your own contractor history and your own management quote.
Worked example — national medians, illustrative operating percentages
Purchase price $343,800 and monthly rent $1,531 are the Census Bureau's Q2 2026 national median asking sale price and median asking rent; vacancy is the same release's 7.3% national rental vacancy rate; the rate is Freddie Mac's 6.71% 30-year PMMS figure for the week ending September 3, 2026; down payment is an illustrative 25% ($85,950). Property tax, insurance, and HOA are left at $0 — no verified national figures exist for any of them. Maintenance is set to 5% of gross rent and management to 8% of effective rent, both illustrative.
| Line item | Amount |
|---|---|
| Monthly mortgage (P&I) | $1,665.56 |
| Effective rent (after 7.3% vacancy) | $1,419.24 |
| Maintenance (5% of $1,531 gross) | $76.55 |
| Management (8% of $1,419.24 effective) | $113.54 |
| Total monthly expenses | $1,855.65 |
| Monthly cash flow | −$436.41 |
Direct output of this calculator's formulas. Annualized: −$5,236.94 cash flow, $14,749.78 NOI, 4.29% cap rate, −6.09% cash-on-cash return, 18.71 gross rent multiplier.
The gap between this result and the plainer investment-cash-flow calculator's result on the same national-median inputs is entirely the maintenance and management lines — this calculator's NOI definition subtracts them; the cash-flow calculator's does not, because it has no fields for either. That is not an inconsistency between two competing tools; it is two calculators answering slightly different questions. This one assumes you will budget for repairs and, optionally, a manager; the other assumes you are pricing the raw financing math and will add operating costs yourself through its generic "other monthly costs" field.
Which input moves the result most
At the national-median inputs above, the mortgage payment ($1,665.56) is still the largest single line, so the financing rate remains the dominant lever — the same one-rate-point swing that reshapes the cash-flow calculator's result reshapes this one by a similar magnitude. But because this calculator layers maintenance and management on top, the two percentage fields compound: raising management from 8% to 10% of effective rent adds roughly $28 a month here on its own, and raising maintenance from 5% to 8% of gross rent adds about $46 more — together enough to turn a marginal deal decisively negative without the purchase price or rent changing at all. Self-managing (setting the management field to 0%) is the single fastest way to see how much of a marginal deal's viability rests on that one assumption.
What this NOI figure still leaves out
- ·Property tax and insurance. Both are input fields with no default — no verified national dollar figure applies broadly enough to default them.
- ·Depreciation. This is a pre-tax cash model. Residential rental buildings depreciate straight-line over 27.5 years under IRS Publication 527; see the rental depreciation calculator for that deduction and the recapture that follows it at sale.
- ·Multi-year rent growth or appreciation. This calculator produces a single-period (monthly/annual) snapshot, not a multi-year hold projection. For that, see the rental property ROI calculator.
- ·Capital expenditures (roof, HVAC, major systems). The maintenance percentage here is routine upkeep as you define it — it is not a reserve schedule for large, infrequent replacements.
Checking a landlord's or agent's pro forma against this model
A pro forma handed to you by a listing agent or a seller is the single most useful document to run back through this calculator's own fields, because the two most commonly inflated inputs — vacancy and management — are exactly the two this tool separates out for scrutiny. If a seller's pro forma shows 0% vacancy, that is worth comparing to the Census Bureau's 7.3% national rate, which, even as a rough proxy, is a real measured figure rather than a marketing assumption. If a pro forma has no management line at all, ask whether the projected cash flow assumes you personally handle every leasing call, maintenance request, and turnover — because this calculator's management field defaults to nothing, not to zero cost, and you are choosing that input, not the tool.
One more benchmark is worth checking the rent field against, if the unit could plausibly house a voucher tenant: HUD's Fair Market Rent for FY2027, the 40th-percentile gross rent HUD uses to set Housing Choice Voucher payment standards by metro. It is not a market median — the Census median asking rent used above is the closer comparison for open-market pricing — but it is a real ceiling for what a voucher will pay, and worth checking separately if that tenant pool is part of the plan.
Why year one rarely matches the model
Almost every rental underperforms its own projection in the first year, and the reasons are consistent enough to plan for.
Acquisition costs land immediately while income starts later, so the first year carries the purchase, any make-ready work and a vacancy before the first tenancy begins. A model that starts collecting rent in month one has already overstated year one by whatever that gap actually was.
First-year maintenance also tends to exceed the steady-state assumption, because a change of ownership is when deferred items surface. Build the first year separately from the ongoing years rather than applying the same reserve to both.
Methodology
The worked example runs this calculator's own formulas against the Census Bureau's Q2 2026 median asking sale price ($343,800) and median asking rent ($1,531), the same release's 7.3% national rental vacancy rate, and the Freddie Mac PMMS 30-year rate for the week ending September 3, 2026 (6.71%). Down payment (25%), maintenance (5% of gross rent), and management (8% of effective rent) are illustrative inputs this calculator asks the user to set — no verified national figure exists for any of the three, and they are labeled as illustrative throughout.
Sources
- US Census Bureau — Housing Vacancy Survey, Q2 2026 — accessed 2026-09-07
- Freddie Mac — Primary Mortgage Market Survey — accessed 2026-09-07
- IRS — Publication 527, Residential Rental Property — accessed 2026-09-07
- HUD User — FY2027 Fair Market Rents — accessed 2026-09-07