Why It Matters
Mortgage offset is how much of your housing payment gets covered by rent from other units. If your piti is $2,000 and the other units bring in $1,800, your offset is $1,800—you're effectively paying $200 for housing. A full offset means you live for free. It's the main reason house-hacking works: your tenants subsidize your mortgage while you build equity.
At a Glance
- What it is: Rental income that covers your share of the mortgage payment
- Why it matters: Reduces or eliminates your housing cost
- Full offset: Rent from other units ≥ your total PITI
- Partial offset: Some of your payment is covered; you pay the rest
- Best case: Offset exceeds PITI = positive cash-flow while living there
Mortgage Offset = Rental Income from Other Units − Your Share of PITI
How It Works
The math. You buy a triplex. You live in unit 1. Units 2 and 3 rent for $1,100 and $1,150. Total rent from "other" units: $2,250. Your piti is $2,100. Mortgage offset = $2,250. You're covered—and have $150 left over for operating-expenses or reserves.
Allocating expenses. Some investors allocate operating-expenses (taxes, insurance, maintenance, vacancy-rate) proportionally. If your unit is 1 of 3, you might assign one-third of expenses to "your" share. That gives a more realistic effective-rent and true offset.
The goal. Full or over-offset means your housing cost approaches zero. You're building equity with someone else's rent. When you move out and rent your unit too, the property becomes a full rental-property with cash-flow.
Financing impact. Low-money-down loans (FHA, conventional owner-occupied) keep PITI lower, making full offset easier to achieve.
Real-World Example
Jake in Cincinnati. Jake bought a fourplex for $320,000 with 5% down. His piti was $2,180. He lived in one unit. The other three rented for $950, $1,000, and $1,050—$3,000 total. After 8% vacancy-rate reserve and his share of maintenance, his effective-rent from the three units was about $2,350. His mortgage offset was $2,350. He paid roughly $0 out of pocket for housing (the surplus covered his unit's share of expenses). He lived for free for 22 months before refinanceing and moving.
Pros & Cons
- Reduces or eliminates housing cost
- Build equity with tenant rent
- Low-money-down financing makes offset easier
- Accelerates path to next property
- Requires living in a multi-unit
- Vacancy reduces offset
- Operating-expenses can eat into offset
Watch Out
- Overestimating rent: Use rental-comps, not wishful numbers
- Ignoring expenses: Factor vacancy-rate, maintenance, capex
- Rate reset: Refinance when you move out can raise payment
Ask an Investor
The Takeaway
Mortgage offset is the engine of house hacking: rental income from other units pays your housing bill. Aim for full or over-offset when you run the numbers. It's how you live for free while building wealth.