About the House Hacking Calculator
House hacking means buying a home — often a duplex, triplex, fourplex or a house with spare bedrooms or an ADU — living in part of it, and renting out the rest. This calculator works out the full monthly cost of owning (principal, interest, property tax, insurance, mortgage insurance and a maintenance reserve), subtracts the rent you collect after vacancy, and shows the net amount you actually pay to live there.
It is aimed at first-time buyers and new investors deciding whether a multi-unit or roommate setup makes sense, and at anyone comparing a house hack with simply renting. Enter what you would otherwise pay in rent to see your monthly savings; if the net cost is negative, the tenants are paying you to live there.
Owner-occupied buyers can often use low-down-payment loans such as FHA (3.5% down on 1–4 unit properties) or conventional 5% down, so mortgage insurance is added automatically whenever the down payment is under 20%. Check local rent levels and lender rules on counting rental income before you buy.
With the default inputs, the your net monthly housing cost is $1,440.22. Change any value above to recalculate instantly.
How to use the house hacking calculator
- 1Enter the purchase price, down payment percentage, rate and term.
- 2Add yearly property tax, insurance and the mortgage insurance rate.
- 3Enter the total monthly rent from the units or rooms you will rent out.
- 4Set a vacancy allowance and a repairs reserve percentage.
- 5Enter the rent you pay now to see your monthly savings.
Formula and method
Principal and interest use the standard amortization formula on the loan (price minus down payment). Mortgage insurance is the yearly rate times the loan divided by 12 and applies only when the down payment is below 20%. A reserve for repairs and capital expenditures is set aside as a percentage of the rent you collect, because tenants create wear that an owner-only home would not.
Rent from the other units or rooms is reduced by the vacancy allowance to reflect months without a tenant. The difference between total ownership cost and collected rent is what you effectively pay to live in the property. Comparing it with the rent you would otherwise pay shows the monthly benefit of the house hack; principal paydown and appreciation are extra wealth on top.
- P&I
- Monthly principal and interest payment
- MI
- Monthly PMI or FHA mortgage insurance
- Reserve%
- Repairs and CapEx set-aside as a % of rent
- Vacancy%
- Share of the year units sit empty
Worked examples
$450k duplex with 5% down
A $427,500 loan at 6.5% costs $2,702.09 a month; tax, insurance, $178.13 of mortgage insurance and a $240 reserve bring the total to $3,720.22. The other unit rents for $2,400, or $2,280 after 5% vacancy, so you pay $1,440.22 to live there — $359.78 less than your $1,800 rent.
Same duplex with 20% down
Putting $90,000 down cuts the loan to $360,000, drops mortgage insurance and lowers principal and interest to $2,275.44. Your net housing cost falls to about $835 a month, saving roughly $965 compared with renting.
$600k triplex renting two units for $3,600
A $570,000 loan at 6.5% costs $3,602.79. With $600 tax, $200 insurance, $237.50 mortgage insurance and a $360 reserve, ownership totals $5,000.29. Two units bring $3,420 after vacancy, so you pay $1,580.29 — about $620 less than renting at $2,200.
Frequently asked questions
What is house hacking?+
House hacking is buying a property you live in and renting out part of it — other units of a small multifamily, spare bedrooms, a basement apartment or an ADU — so that the rent offsets or fully covers your mortgage and housing costs.
Can I use an FHA loan to house hack?+
Yes. FHA loans allow 3.5% down on owner-occupied properties with one to four units, provided you live in one of the units as your primary residence, typically for at least a year. FHA loans carry mortgage insurance premiums.
Do lenders count rent from the other units as income?+
Often they do. For 2–4 unit owner-occupied purchases, lenders commonly count about 75% of the expected rent from the other units (based on leases or an appraiser rent schedule) toward qualifying income. Rules vary by loan program and lender.
What vacancy and repair allowance should I use?+
A 5%–8% vacancy allowance (roughly two to four weeks a year) is a common starting point, and 5%–10% of rent each for repairs and capital expenditures. Older buildings or student rentals usually need higher figures.
Is house hacking better than renting?+
It usually lowers your monthly cost and builds equity, but you become a landlord living next to your tenants, you need a down payment and reserves, and you carry repair risk. Compare the net cost here with your current rent and the time you are willing to put in.
Results are estimates for educational purposes and are not financial advice. Rates, fees and terms vary — confirm with your lender or a licensed advisor before making decisions.