House Hacking Calculator

What is House Hacking?

House hacking means buying a property, living in part of it, and renting out the rest — a spare bedroom, a basement unit, or another unit in a duplex or triplex. The rent you collect offsets your housing costs, sometimes covering the entire mortgage payment.

This calculator uses the same mortgage math as our standard $\text{Mortgage Calculator}$ — home price, down payment, loan length, and rate — then layers rental income and vacancy on top to show how a tenant changes your numbers.

Vacancy Rate and Effective Rental Income

No rental is occupied 100% of the time. Between tenants, a vacancy rate estimates how often the unit sits empty — during those months, you cover the full mortgage payment yourself. To plan realistically, we spread that risk across every month using an average, or "effective," rental income:

For example, $1,200/mo rent with a 10% vacancy rate averages out to:

That $1,080 is what we use to estimate your typical month — in an actually vacant month you'd owe the full payment, and in an occupied one you'd collect the full rent.

Two Ways to Use the Rent

Once you calculate, use the "Apply rent as an additional payment" toggle in your results to switch between two strategies for what happens to the rent you collect:

Offset Your Payment (toggle off, default)

The rent is applied directly against your mortgage payment, so you only pay the portion the tenant doesn't cover. The loan amortizes exactly like a normal mortgage — same payoff date, same total interest — only your out-of-pocket share shrinks.

If effective rent exceeds your mortgage payment, this turns negative — the property pays you. Your results show these monthly and lifetime savings directly.

Apply Rent as an Additional Payment (toggle on)

With this toggle on, you keep paying the full mortgage payment out of your own pocket every month, and the rent you collect is instead applied as extra principal — the same way a manual extra payment works on the standard Mortgage Calculator. That accelerates the amortization schedule, shortening the loan and cutting total interest.

Each period, the extra principal reduces the balance the same way an additional payment would:

This trades a lower monthly cost today for a faster, cheaper payoff overall — you're effectively using your tenant's rent to buy down the loan instead of pocketing it as cash flow. Your results show the total interest saved and exactly how much earlier you'll pay off the loan.

Things to Consider

• Owner-occupancy requirements — many low-down-payment loan programs require you to live in the property for at least a year
• Rental income taxes — rent you collect is typically taxable income, though you may be able to deduct a share of expenses
• Maintenance and turnover — tenants add wear and tear, and vacancies between tenants can run longer than your estimate
• Landlord responsibilities — screening tenants, handling repairs, and knowing your local landlord-tenant laws all come with the territory

None of these are modeled explicitly here — this calculator focuses on the mortgage and rental income math so you can layer in your own assumptions about taxes, upkeep, and local regulations.

Key Takeaway

House hacking turns a portion of your mortgage into someone else's rent payment. Whether you use that rent to lower your monthly cost today or to pay off the loan faster, the underlying amortization is identical to a standard mortgage — the tenant just changes who's footing the bill.