Forget “cash flow” for a second. This is the number that actually changed my life.
Most real estate content trains you to obsess over cash flow, does the property make money each month? For a house hacker, that’s the wrong first question, and chasing it will talk you out of good deals.
The number that matters is your effective housing cost: what you actually pay to live there each month after your tenants chip in.
The formula
It’s almost embarrassingly simple:
Effective housing cost = your total monthly housing payment − rent collected from the other units.
That’s it. Your mortgage, tax, insurance, and mortgage insurance, minus what your tenants pay you.
My real numbers
My total monthly housing payment (PITI) on the duplex is about $2,880. While I live here:
- Upstairs tenant pays $1,200
- Basement short-term rental averages roughly $1,083
So $2,880 − $2,283 = an effective housing cost of about $600/month.
Before the duplex, I was paying $1,500/month to house myself. The house hack cut that by roughly 60%, and it did it while I built equity on a $470,000 asset instead of paying down nothing.
Why this beats “cash flow”
If you only looked at my property’s cash flow, you’d see a loss, because I live in one unit rent-free, a third of the building produces no income. On paper the property “loses” money. In reality, I win by hundreds of dollars a month. The arbitrage doesn’t show up on the property’s books. It shows up on mine.
That’s why effective housing cost is the house hacker’s true scoreboard. Cash flow is for pure rentals. Effective housing cost is for people living in the deal.
What counts as “good”
There’s no universal number, but a useful test: compare your effective housing cost to what you’d pay to rent a comparable place. If you’re housing yourself for meaningfully less and building equity, the deal works, even if the property’s cash flow line looks ugly.
A bonus most people forget: the day you move out, every unit rents, and the property’s standalone math usually flips positive. You were never really losing money. You were buying a discount on your own rent and an asset at the same time.
Run yours
The calculator computes this directly, plug in a real listing and the expected rents, and it’ll show your effective housing cost in seconds. That single number tells you more about a house hack than any cash-flow figure ever will.
Tracking a listing right now? I’ll run the numbers with you.
This number only matters in context — here’s what house hacking is.
The First-Property Bundle
The step-by-step playbook, the six-calculator deal-analyzer toolkit, and the down-payment-assistance finder — the exact system I used to go from a van to a duplex.
Pay what you want. Name your price — and if money’s tight, take it for less.
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The five-stage plan I used to go from living in a van to owning a duplex, no rich parents required.