How accurate should my rental income estimate be before making an offer?

Your estimate should be based on actual comparable rents in the neighborhood — not the current owner’s claim, not a website estimate, not wishful thinking. Research 5–10 active comparable listings on Zillow and Apartments.com. Use the 25th percentile rent as your conservative base case, not the median or maximum.

What vacancy rate should I use in my calculations?

Use 5% minimum for a well-located property in a tight rental market. Use 8–10% for markets with higher vacancy rates or for properties with characteristics that may slow leasing (location, condition, price). Never assume 0% vacancy in your underwriting — no property is continuously occupied.

How do I estimate property taxes before making an offer?

County property tax records are public. Search your county assessor’s website for the property address to find current assessed value and annual tax bill. Note that purchase at a higher price than current assessed value may trigger reassessment in some states (notably California under Prop 19 exceptions — reassessment is more common elsewhere). Your lender will also verify property taxes during underwriting.

What should I include in the maintenance reserve?

Standard maintenance reserve: 1% of property value per year ($267/month on a $320,000 property). This covers routine repairs, appliance replacement, touch-up maintenance, and occasional larger items (water heater, roof patch). Capital expenditures (full roof, HVAC system) are covered separately by a 0.5% CapEx reserve. Combined, budget 1.5% of property value per year for reserves.

What is a good effective monthly housing cost for a house hack?

Any effective monthly housing cost below your current rent or local market rent for a comparable unit is a win. An effective cost of $0 (break-even) or negative (cash flow positive) is exceptional — achievable in the best markets with optimal unit mixes. Most house hackers target 40–70% reduction in housing cost from their current rent as a realistic success benchmark.

How to Run Accurate House Hacking Numbers Before You Buy

The single most important skill in house hacking is running accurate numbers before making an offer. Overestimating rental income or underestimating expenses leads to deals that underperform, drain reserves, and create financial stress instead of savings. This guide gives you the five essential calculations to run on any house hack candidate property before submitting an offer.

Calculation 1: Full Monthly Mortgage Cost (PITI)

Principal + Interest + Taxes + Insurance = PITI. Use a mortgage calculator with the actual loan amount, current interest rate quote (not a guess), actual property tax rate from county records, and actual insurance quote (call an agent for a quote before closing). PITI is your baseline cost regardless of tenant income.

Calculation 2: Net Rental Income (Not Gross)

Gross rent × (1 − vacancy rate) = Effective Gross Income. Then subtract property management (if using), and maintenance reserve (1% of property value/year). The result is net rental income — the actual cash you can count on to offset your mortgage. Never use gross rent as your income assumption.

📊Net Rent Calculation Example

Duplex unit rents for $1,300/month. Vacancy 5%: $1,235 EGI. Maintenance reserve (1% of $320K ÷ 12 = $267, split 50% to rental unit): $133. Net income from rental unit: $1,102/month. Not $1,300. This $198 difference matters significantly in a tight cash flow scenario.

Calculation 3: Effective Monthly Housing Cost

Effective Housing Cost = PITI − Net Rental Income. This is your actual monthly out-of-pocket. If the result is negative, the property generates positive cash flow (you’re paid to live there). If positive, it’s your effective rent equivalent. Compare this to your current rent and to market rent for a comparable unit to evaluate the deal’s value.

Calculation 4: Cash-on-Cash Return

Cash-on-Cash Return = (Annual housing cost savings OR annual positive cash flow) ÷ Total cash invested × 100. At $800/month savings and $25,000 invested: ($800 × 12) ÷ $25,000 = 38.4% cash-on-cash return. This metric lets you compare house hacking to other investment opportunities on an apples-to-apples basis.

Calculation 5: 5-Year Equity and Appreciation Projection

Project your 5-year wealth gain: Principal paydown (use an amortization schedule for years 1–5) + Appreciation (purchase price × (1 + appreciation rate)^5 − purchase price) + Housing cost savings. Sum these three to see the total 5-year financial benefit of the house hack. This projection anchors the decision in long-term wealth rather than monthly cash flow alone.

Run All 5 Calculations on Your Target Property

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Frequently Asked Questions

How to Run Accurate House Hacking Numbers Before You Buy

Calculation 1: Full Monthly Mortgage Cost (PITI)

Calculation 2: Net Rental Income (Not Gross)

Calculation 3: Effective Monthly Housing Cost

Calculation 4: Cash-on-Cash Return

Calculation 5: 5-Year Equity and Appreciation Projection

Frequently Asked Questions

Frequently Asked Questions

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House Hacking a Duplex: Step-by-Step Numbers for Your First Deal

7 Common House Hacking Mistakes That Kill Cash Flow