By Jessica Martinez, Contributing Writer, Business & FinancePublished July 7, 2026
Monthly cash flow equals net operating income minus debt service: on $2,000 rent at 6% vacancy with the expense list above and a $1,050 mortgage payment, this calculator returns $236 a month, well above the negative $50 the 50% rule alone would suggest. NOI is effective rent minus every operating cost except the mortgage, taxes, insurance, maintenance and management fees. Subtract the loan payment from NOI and what is left is cash flow, the only one of these figures that actually shows up in a bank account.
Why itemizing beats a flat percentage
A flat expense assumption is fast but blind to what actually drives a property's cost structure. Two identical rents in two different states can carry very different tax bills. A property with no HOA and a self-managed landlord looks nothing like one with a $300 monthly HOA and a hired property manager, even at the same rent. Itemizing forces each of those differences into its own line instead of averaging them away.
Debt service deserves its own line too, separate from operating expenses. NOI, by definition, ignores financing entirely, which is what makes it comparable across an all-cash buyer and a heavily leveraged one. Cash flow only enters the picture once the actual loan payment gets subtracted, which is why this calculator keeps the two steps visually distinct instead of folding everything into one lump expense total.
The default deal, line by line
This calculator loads with $2,000 in monthly rent, 6% vacancy, and the expense list shown in the panel above. Here is exactly how those numbers stack up:
| Line item | Monthly amount |
|---|---|
| Effective rent (after 6% vacancy) | $1,880 |
| Property taxes | $225 |
| Insurance | $92 |
| Maintenance | $108 |
| Management fee (9% of effective rent) | $169 |
| Total operating expenses | $594 |
| Net operating income | $1,286 |
| Debt service (P&I) | $1,050 |
| Monthly cash flow | $236 |
Total operating expenses here land at roughly 30% of gross rent, well under the 50% rule's assumption. That gap is common on properties without a large HOA bill or an aging roof and HVAC system waiting to be replaced. It is also exactly why the 50% rule works better as a red-flag check than as a substitute for the real math.
What this calculator does not cover
This is a pre-tax, cash-basis figure. It does not account for depreciation, income tax on rental profit, or a separate capital reserve for a future roof or HVAC replacement, which many landlords budget outside of routine maintenance. A property that clears this cash flow test can still need a large one-time outlay in a bad year, so treat a healthy monthly number as a floor to build a reserve on top of, not a promise that nothing else will come due.
When negative cash flow still might be worth it
Negative monthly cash flow is not an automatic disqualifier, though it deserves a clear-eyed reason before anyone accepts it. Some buyers take a small monthly loss on a property in a fast-appreciating area, betting that equity growth and rising rent over a few years will outpace what they are covering out of pocket today. That can work, but it is a different bet than buying for cash flow, and conflating the two is how a landlord ends up subsidizing a property indefinitely instead of a few planned years.
The honest version of that bet involves a number, not a feeling: how many months of negative cash flow can the owner actually absorb before rent increases or a refinance are expected to flip the number positive, and what happens if that timeline slips by a year. A property that only pencils out if every assumption goes right is not a safe negative-cash-flow bet, it is a property that needs a lower purchase price or a bigger down payment before it deserves an offer.
FAQ
What is a good monthly cash flow for a rental property?
There is no single dollar figure that applies everywhere, since a small condo and a large single-family home carry very different expense loads. Many landlords look for at least $100 to $200 in monthly cushion per unit after every line item is paid, enough to absorb a slow month without going negative, but the right target depends on the property's price, financing and your own risk tolerance.
Is the 50% rule accurate for estimating expenses?
It is a rough screening shortcut, not a precise formula. The 50% rule assumes operating expenses, excluding the mortgage, run close to half of gross rent. Newer properties, properties without a management fee, or properties in low-tax states often run well under 50%, while older buildings with deferred maintenance can exceed it. Use it as a sanity check against your itemized total, not a replacement for one.
What counts as debt service in a cash flow calculation?
Debt service is the monthly principal and interest payment on the mortgage. It does not include property taxes or insurance even when a lender escrows those into one combined payment; this calculator keeps taxes and insurance in the operating expense line so the NOI figure stays comparable across properties with different loans.
What is the difference between NOI and cash flow?
NOI is effective rent minus operating expenses, with the mortgage left out entirely. Cash flow is NOI minus debt service, the number that actually reflects what a financed property returns each month. Two investors buying the same property with different loans will see identical NOI but different cash flow.