How Mortgage Offset Works in Practice
Rental income doesn’t literally reduce your mortgage payment — you still owe the bank the full PITI (principal, interest, taxes, insurance) each month. What changes is how much of that payment comes from your pocket vs. from tenant payments. If your total mortgage cost is $2,500/month and you collect $1,800 in rent, your out-of-pocket is $700 — the offset amount.
Mortgage offset by house hacking strategy
| Strategy | Monthly Mortgage | Rental Income | Your Cost | % Offset |
|---|---|---|---|---|
| 1 room in SFH | $2,200 | $700 | $1,500 | 32% |
| 2 rooms in SFH | $2,200 | $1,400 | $800 | 64% |
| Basement unit in SFH | $2,200 | $1,100 | $1,100 | 50% |
| Duplex (live in one unit) | $2,800 | $1,400 | $1,400 | 50% |
| Triplex (2 units rented) | $3,200 | $2,800 | $400 | 88% |
| Fourplex (3 units rented) | $3,600 | $4,200 | $0 + $600 profit | 100%+ |
A 100% mortgage offset — where rental income fully covers your monthly PITI — is achievable in most markets with a triplex or fourplex using FHA financing. In markets with higher rents relative to purchase prices, even a duplex or large SFH with 2 roommates can reach this threshold.
The Math to Zero Housing Cost
To achieve zero effective housing cost, your rental income must cover: mortgage P+I + property taxes + insurance + maintenance reserve + vacancy allowance. Example: $2,500/month total needed. To cover this fully, you need rental income of at least $2,500/month — which requires either multiple units, premium rentals, or high-demand short-term rental income.
Market Impact on Offset Potential
Markets with high rent-to-price ratios are best for mortgage offset. In Columbus, OH, a $250,000 duplex might generate $2,800/month in rent (1.12% ratio) — easily covering a $1,800/month mortgage. In San Jose, CA, a $900,000 duplex might generate $4,500/month in rent (0.5% ratio) — covering less than half the $5,500/month payment. Location dramatically affects the achievable offset percentage.
Including Utilities in the Offset Calculation
Some house hackers rent rooms or units including utilities, others charge separate utilities. Including utilities allows higher rent but adds cost and variability. If you charge $900/room inclusive vs. $800 exclusive, you need to cover the utilities from the $100 premium. Calculate the marginal utility cost per additional person ($40–$80/month typically) to determine which structure is more profitable.
Calculate Your Mortgage Offset Percentage
Enter your mortgage costs and rental income to see exactly how much your tenants cover.