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Strategy

The 50% rule: estimating expenses before you have real numbers

Updated 2026-07-07

The 50% rule says that over time, a rental property's operating expenses will average about 50% of its gross rent. Rent for $2,000/mo, expect about $1,000/mo to go to running the property, before the mortgage. What's left after expenses is your estimated NOI; subtract the loan payment and you have a first-pass cash flow number in your head.

Est. NOI = Gross Rent × 50%   ·   Est. Cash Flow = (Gross Rent × 50%) − Monthly P&I
The 50% covers operating expenses only. The mortgage payment is never inside it. That's the most common misreading.

Try it

Monthly rent
Monthly P&I payment
Est. expenses / mo
,
Est. NOI / mo
,
Est. cash flow / mo
,

What's inside the 50%

The rule bundles every cost of operating the property: property taxes, insurance, vacancy, repairs, capital-expenditure reserves (roof, HVAC, water heater), property management, and any owner-paid utilities. It works as a long-run average because the lumpy items (a vacancy month, a $9,000 roof) even out across years, even when any single year looks nothing like 50%.

Where the 50% rule breaks

  • High-tax, high-insurance markets run over. In parts of Texas, New Jersey, or coastal Florida, taxes and insurance alone can eat 25 to 35% of rent before a single repair.
  • Low-rent properties run over. A furnace costs the same in a $900/mo rental as in a $2,400/mo one. Fixed costs make cheap units run well past 50%, which is exactly where 1%-rule screening tends to point.
  • Old housing stock runs over; new builds run under. Age drives repairs and capex more than any average captures.
  • "I'll self-manage" doesn't delete the management line. Your time has a cost, and the day you scale or move, the 8 to 10% comes back. Underwrite as if you pay it.

50% is a placeholder for real numbers, not a substitute for them.

From placeholder to real numbers

The 50% rule is for the minute when you have a rent figure and nothing else. Before you offer, replace it: the actual tax bill is public record, an insurance quote takes a phone call, and vacancy rates are knowable by market. BuyBox underwrites with itemized expenses, taxes, insurance, vacancy, repairs, capex, and management as separate lines, and shows how each flows into NOI, DSCR, and cash flow. Hover any number to see the formula and inputs behind it. The full walk-through is in How to analyze a rental property.