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About House Hacking Effective Rent Calculator: Housing Cost Offset
Estimate your effective personal housing cost after rent received from roommates, units or other occupants.
Change the example inputs to match a scenario and review the methodology and limitations before using the result in a decision. Calculations run locally in your browser.
How the calculation works
Gross monthly housing cost
Mortgage + property tax & insurance + HOA + utilities + maintenance reserve + other costs.
Effective rental income
Expected monthly rent received × (1 − vacancy allowance % ÷ 100).
Effective housing cost & offset
Effective cost = gross housing cost − effective rent income; cost offset % = (effective rent income ÷ gross housing cost) × 100.
How to use this calculator
- 1Replace the example values with internally consistent inputs.
- 2Review all result cards and any not-applicable state.
- 3Compare multiple scenarios and verify important assumptions independently.
Understanding the result
Effective monthly housing cost represents your net out-of-pocket housing expense after crediting vacancy-adjusted rental income.
If effective rental income exceeds gross housing costs, effective housing cost is legitimately negative, meaning tenant rents exceed living overhead and generate net surplus cash flow.
The cost offset percentage shows how much of your total homeownership overhead is covered by occupant rents.
Important limitations
- Outputs are planning estimates and do not include every provider, accounting, financing, tax, legal, or operational factor.
- Invalid divisions are shown as not applicable rather than NaN or Infinity.
- This is a cash-flow planning calculation, not a complete investment return model.
- Principal paydown, appreciation, taxes and transaction costs are excluded.
- Rental income and vacancy are estimates.
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Frequently asked questions
What is house hacking?
House hacking is a real estate strategy where an owner occupies a primary residence while renting out rooms, additional units (duplex/triplex/ADU), or space to generate income that offsets living costs.
Can effective housing cost be negative?
Yes. If rental income from tenants exceeds total monthly housing expenses, your net housing cost is negative, meaning you live for free and pocket surplus cash flow.
Why is a vacancy allowance included?
Tenants occasionally move out. A conservative vacancy allowance (e.g. 5%) accounts for turnover gaps between tenant occupancies.
Should I include maintenance reserves?
Yes. Budgeting a monthly reserve for repairs, roofs, and HVAC replacements prevents unexpected maintenance from overwhelming your personal budget.
Does this calculate loan principal paydown?
No. The mortgage input is treated as an out-of-pocket cash outflow. Equity accumulation from amortizing your loan principal is an additional wealth benefit.
Is my personal financial information stored on any server?
No. The calculator executes entirely on your device.
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