House Hacking on Zillow: How to Underwrite Your First Deal
House hacking math on Zillow—live-in vs. rent units, FHA-friendly assumptions, and how to analyze your first owner-occupied rental with Realy before you make an offer.
House hacking—living in one unit while tenants cover part or all of the mortgage—is how many investors buy their first property. Zillow is where most people find those deals. The trick is underwriting your actual housing cost reduction, not just gross rent.
What Is House Hacking?
Common formats (1–4 units, Realy's sweet spot):
| Type | You live | Tenants pay |
|---|---|---|
| Duplex | One side | Other side |
| Triplex / fourplex | One unit | Remaining units |
| SFR with ADU | Main house | Accessory unit |
| Room rental | One bedroom | Other rooms (check local rules) |
Goal: Lower or eliminate your personal housing payment while building equity.
Metrics That Matter for House Hacking
Standard investor metrics still apply, but prioritize:
| Metric | Why |
|---|---|
| Monthly cash flow (whole property) | Does rent cover PITI + expenses? |
| Your net housing cost | PITI − tenant rent = what you actually pay to live |
| CoC on down payment | Lower down (FHA 3.5%) amplifies CoC |
| DSCR | Lenders may require ≥ 1.0 on non-owner portion |
Your Net Housing Cost = Monthly PITI + Expenses − Tenant Rent Collected
If tenant rent covers 100% of PITI, you "live free" while owning.
Step 1: Find Candidates on Zillow
Search filters:
- Multi-family (duplex, triplex) OR SFR with ADU keywords
- Price within FHA/conventional limits for your county
- Neighborhoods where you would actually live (non-negotiable)
Open Realy analyzer on search results to rank by cash flow potential.
Step 2: Adjust Realy Assumptions for House Hacking
| Setting | House hack adjustment |
|---|---|
| Down payment | 3.5–5% (FHA/conv owner-occ) vs. 20% investor |
| Interest rate | Owner-occupied rate (often lower than DSCR) |
| Loan duration | 30Y typical |
| Vacancy | Lower if you self-manage on-site |
| Management | 0% (you're the landlord on-site) |
| Insurance | Owner-occupant policy—quote separately |
| HOA | Confirm house hack / rental allowed |
In Realy, change down payment from 20% to 3.5% or 5% and watch CoC and cash flow shift dramatically.
Step 3: Model "Your" Number, Not Just Property CoC
Example: Duplex, $350,000, you live in unit A, rent unit B for $1,800/mo
| Line item | Monthly |
|---|---|
| PITI (5% down, owner-occ rate) | ~$2,400 |
| Expenses (tax, ins, maint) | ~$650 |
| Total cost | ~$3,050 |
| Unit B rent | −$1,800 |
| Your net housing cost | ~$1,250 |
Compare $1,250/mo to your current rent payment—that is your real return.
Step 4: Run the First-Timer Checklist
Before offering:
- FHA/conv eligible? (condition, price, occupancy intent)
- 1-year owner-occupancy requirement understood
- Separate meters / lease structure planned
- Rent comps for tenant unit only
- Budget for shared maintenance
- Exit plan after moving out (convert to full rental?)
Full checklist: First rental property guide.
Step 5: Use Realy on the Listing Page
On the Zillow detail page, Realy's mini side panel lets you tweak assumptions while scrolling photos and floor plans—critical for evaluating whether the tenant unit layout actually rents.
Click Detailed analysis to save/share your house hack model.
Common House Hack Mistakes
- Using 20% investor down when you'll use FHA—misprices the opportunity
- Ignoring your unit's market rent if you moved out later
- Skipping HOA rental rules in condos/townhomes
- Underestimating capex on older duplex stock
Start Your First House Hack Search
- Install Realy
- Search duplex/triplex on Zillow in your target area
- Set 3.5–5% down in assumptions
- Rank by cash flow; model your net housing cost
Related: How to find cash-flowing rentals · CoC formula