The Number the Facebook Posts Never Show You
Every house hacking post has the same headline: the tenant pays the mortgage. What they almost never show is the full monthly cost, with taxes, insurance, mortgage insurance, repairs, and the month the unit sits empty, and what’s left for you to pay after the rent comes in.
This calculator gives you that number for a real listing. Put in the price, your loan, and the rent, and it shows your monthly share, how that compares to renting and to buying a regular house, and whether a lender is likely to see the deal the way you do.
Short version: Your “monthly share” is the full cost of owning the property, including maintenance, savings for big repairs, and vacancy, minus the rent your tenants pay. At 2026 rates around 7%, that share is usually positive, meaning the rent covers part of your housing cost, not all of it. Compare it to two things: what renting a similar place would cost, and what carrying the whole property yourself would cost. Lenders generally count only 75% of the rent, and FHA loans on three- and four-unit homes must pass a self-sufficiency test that many properties fail at today’s rates. If you can do your own repairs, turn on that option to see what it saves you.
For the full picture behind these numbers, including the loan rules, taxes when you sell, and what it’s like living next to your tenants, read House Hacking: What Facebook Won’t Tell You.
How to Fill It In
The property. Pick the type of house hack: renting rooms in a single-family home, or a duplex, triplex, or fourplex where you live in one unit. Enter the rent for each unit or room you’ll rent out. Then enter what it would cost to rent a place like yours, which is the number the calculator compares against.
The loan. Choose conventional, FHA, or VA, then set the down payment and interest rate. Mortgage insurance fills in automatically. You can type your lender’s actual rate over it. For FHA and VA loans, the upfront fee is added to the loan the way it usually is in real life. If you’re buying a property that needs work, add the cash you’ll spend on repairs so it shows up in your cash to close.
Monthly costs. Property taxes, insurance, and any utilities you pay for your tenants are straightforward. Get a real insurance quote if you can, since policies for multi-unit homes often cost more than a standard homeowners policy. The other three lines are the ones most people skip:
- Maintenance and repairs is set as a share of the total rent all units would bring in, including yours.
- Big-ticket savings is money you set aside each month for roofs, furnaces, and water heaters, so a $9,000 replacement doesn’t land on a credit card.
- Vacancy covers the month or so a unit sits empty between tenants.
Doing your own repairs. If you’re handy, flip the “I do my own repairs” switch and set how much of the maintenance budget you’d save. Big-ticket replacements stay in the budget either way, since even a good tradesperson pays for the new roof.
Plug in a real listing and see what living there would actually cost you each month after your tenants’ rent, with the maintenance, repair savings, and vacancy that the social media math leaves out. Then compare it to renting and to buying a regular house, and check whether a lender is likely to see the deal the way you do.
Reading Your Results
Your monthly share is the headline number: what living there costs you each month after rent, in the first year.
Compared to renting shows whether you'd pay more or less than renting a place like yours. It also shows the gap after counting the part of your payment that goes to principal, since that's money you keep as equity rather than money gone.
Compared to buying it with no tenant shows what the rent saves you over carrying the whole property yourself. For most people this is the honest comparison, since the real alternative to house hacking is usually buying a regular home, not renting forever.
The lender reality check flags the things that can stop a deal before it starts: a down payment below the program minimum, how much of the rent a lender will actually count, the FHA self-sufficiency test for three- and four-unit homes, and whether a conventional loan fits under the 2026 conforming limits.
Where the money goes lists every line, so you can see exactly what's driving the number and check it against your own math.
The default numbers are the duplex example from the house hacking article: a $450,000 duplex with 5% down at 7.25%, with the other unit renting for $1,800.
Before You Make an Offer Based on This
A calculator is only as good as what you put in it. Before you rely on the result:
- Check the rent. Look at real listings for similar units nearby, not what the seller says the unit "could" rent for.
- Get real quotes. Property taxes often change after a sale, and insurance for a multi-unit home can surprise you.
- Confirm the units are legal. A basement apartment without permits may not count for the lender, and may not be legal to rent at all.
- Ask your lender how they'll count the rent and what reserves they'll want. Mortgage preapproval covers what to bring.
For more on the loan side, see FHA vs. conventional loans, PMI explained, and VA loan benefits. If you plan to move out later and rent the whole property, run it through the rental property calculator too, and budget for the hidden rental costs most first-time landlords miss.
This article is for general informational purposes only and isn't financial, legal, insurance, or tax advice. For guidance specific to your situation, talk to a licensed professional.
Frequently Asked Questions
Add up the full monthly cost of owning the property: principal and interest, property taxes, insurance, mortgage insurance, any HOA, utilities you pay, maintenance, savings for big repairs, and a vacancy allowance. Then subtract the rent your tenants pay. What's left is your monthly share of the housing cost.
Because those costs are real even when they don't show up every month. Repairs, replacements like a roof or furnace, and empty months between tenants are where most house hacking math goes wrong. Leaving them out makes a deal look better than it is.
For two- to four-unit homes, lenders generally count 75% of the expected rent from the other units. With less than a year of landlord experience, many will only let that rent offset the property's own payment. Rent from roommates in a single-family home is often counted little or not at all.
For three- and four-unit homes bought with an FHA loan, 75% of the estimated rent for all units, including the one you live in, must cover the full monthly payment with taxes, insurance, and mortgage insurance. If it doesn't, FHA won't finance the property regardless of your income.
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Sources
https://selling-guide.fanniemae.com/sel/b3-3.8-02/rental-income-subject-property
https://themortgagereports.com/107690/fannie-mae-introduces-5-down-payment-option-for-multifamily-homes
https://www.financewonk.com/references/conforming-loan-limits
https://www.thefederalsavingsbank.com/Blog/federal-housing-administration-fha-self-sufficiency-test-for-3-4-unit-homes-what-buyers-should-know/
https://www.hud.gov/sites/dfiles/OCHCO/documents/2023-05hsgml.pdf
https://www.va.gov/housing-assistance/home-loans/funding-fee-and-closing-costs/