How to Use a House Hacking Calculator (Step by Step)

A house hacking calculator takes the purchase price, down payment, interest rate, taxes, insurance, and the rent from the unit you won’t live in, and turns them into three numbers, your monthly out-of-pocket cost, your cash flow if you later move out, and your cash-on-cash return. Below I run a $167,000 Cleveland duplex through every field so you can follow along.

I built the calculator on this site after underwriting dozens of listings by hand. This is the exact walkthrough I use when a new listing catches my eye.

---

Before I bought my duplex, I ran every candidate through a spreadsheet, and I made enough mistakes doing that to eventually build the free house hacking calculator on this site. The tool does the math in about two minutes, but the output is only as good as what you feed it. This post walks through every field: what to enter, where to find each number, and how to read the results once they appear. If you just want the tool, go straight to it. It needs no account and no email address.

Have three numbers ready before you start

Before you start, have the listing price, the county tax bill, and a realistic rent for each unit cross-checked against HUD Fair Market Rents.

A listing price, the property tax bill, and a realistic rent for each unit. The price comes from the listing or from the offer you plan to make. The tax bill is on the county assessor site, and I trust that over whatever estimate the listing shows. For rents, look at asking rents for comparable units within a mile or so, then cross-check against HUD Fair Market Rents for your metro so one optimistic listing does not set your whole model.

Step 1: Property and financing

Enter price, down payment (FHA allows 3.5 percent on one to four units), rate, term, real tax and insurance figures, and closing costs of 2 to 5 percent.

Purchase price is the listing price or your planned offer. Down payment is where house hacking gets reachable: an owner-occupied FHA loan allows 3.5 percent down on properties with one to four units, which is how I bought a $470,000 duplex with about $16,000 down. Interest rate comes pre-filled with the current Freddie Mac 30-year weekly average. Replace it with your actual quote once a lender gives you one. Loan term stays at 30 years for most first deals. Property tax and insurance should be the real annual figures, and note that a policy on a two-to-four-unit building costs more than a single-family homeowner policy, so get a real quote if you can. Mortgage insurance applies at low down payments. On FHA loans it is called MIP and the calculator includes it in the payment. Closing costs usually land between 2 and 5 percent of the purchase price.

Step 2: Rental income

Enter conservative rent for the other unit, about 87.5 percent of comparable asking rent, plus market rent for your own unit to power the fully-rented view.

Rent from the other unit is the engine of the whole deal, so be conservative. I model 87.5 percent of typical asking rent for comparable units rather than the best number I can find. Market rent for your unit is what your own unit would fetch if you rented it out. It does not change what you pay while living there, but it powers the fully-rented view, which tells you what the property becomes after you move out.

Step 3: Operating assumptions

Set vacancy at 8 percent, maintenance at 12 to 15 percent of rent on older buildings, and management at zero while you live there, then rerun at 8 to 10.

Vacancy at 8 percent is roughly one empty month per year, a fair default for a stable rental market. Maintenance is the field people underestimate most. On older buildings I set 12 to 15 percent of rent, not 5. My 1925 duplex produced a $20,000 boiler in year one, and a calculator assuming 5 percent would have told me a comforting lie. Management can sit at zero while you live there and self-manage, but run a second pass at 8 to 10 percent to see what the deal looks like once you move out and hire it out.

Step 4: Reading the results

Results show the payment breakdown, your effective housing cost while you live there, and cash flow, cap rate and cash-on-cash return when fully rented.

The output comes in three parts. The monthly payment breakdown shows principal and interest, mortgage insurance, taxes, and insurance, so you can see exactly what the bank collects. While you live there is the house-hacking view. Its headline number is your effective housing cost: what you personally pay each month to live in the property after the other unit contributes rent. For me this is the single number that decides whether a house hack works. When fully rented shows what the property does on its own after you move out: monthly cash flow, cap rate, and cash-on-cash return. If those last terms are new, I keep a plain-english guide to calculating rental cash flow and a separate look at what counts as a good cash-on-cash return.

Worked example on a Cleveland duplex

A $167,000 Cleveland duplex at 3.5 percent down costs $1,636 a month; $1,069 rent from the other unit, less a vacancy and repair holdback, leaves an effective housing cost near $821.

Take the Cleveland duplex the published Cleveland figures describe, the median deal in my screen, at $167,000. It is cheaper than most of what survives: the metro entry price, meaning the 25th percentile of surviving listings, is $169,997, and the median surviving listing is $210,000.^[S1] With 3.5 percent down on an FHA loan at 6.66 percent, that is $5,845 down plus about $4,676 in closing costs, so roughly $10,521 to get the keys. The loan is $163,975 once the 1.75 percent upfront mortgage insurance premium is financed in, and the payment stack is about $1,054 principal and interest, $75 annual mortgage insurance, $319 property tax and $189 insurance, for $1,636 a month. The other unit brings in about $1,069 a month. The Foothold model behind the Cleveland figures holds back 23.8 percent of that for vacancy and repairs, so $815 actually goes toward the payment and the effective cost lands near $821 a month. The calculator’s live-in number counts the full rent, about $567 here, so set the repair money aside on top of it. A comparable place in the same metro would run about $1,154, so owning instead of renting keeps roughly $333 a month in your pocket.

That spread is the entire thesis of this site, and the metro breakdown shows where else the math clears.

Two habits that keep the numbers real

Model maintenance high on old buildings, and distrust any result that beats every comparable real deal in the area; an expense line is probably missing.

• Model maintenance high. Old buildings tell you their age through repair bills, and the reserve line is where a pretty projection becomes a bad month.
• Distrust a great-looking result. If your projected cash flow beats every comparable real deal in the area, an expense line is probably missing. Rerun it meaner.

Why the calculator stays free

The calculator stays free and ungated because a tool built to capture leads is less useful; an optional paid bundle exists, but the tools never gate.

I got obsessed with these numbers and bought a duplex with them. The tools cost me nothing to keep up, and a free, ungated calculator is more useful to you than one designed to capture a lead. If you later want the full step-by-step version, there is an optional paid bundle, a playbook plus a deal-analyzer toolkit that go deeper than any single calculator, but the tools on this site stay free either way.

Keep going

Open the free house hacking calculator and run a real listing through the steps above. To model a longer hold, the projection tool runs the deal year by year, and the roadmap tells you whether your finances are ready to start. New to the whole idea entirely, start with house hacking explained in plain english. And if you are comparing tools, I wrote up the best free house hacking calculators and a free BiggerPockets calculator alternative with notes on when a free tool is enough.

---

Found a deal you want a second opinion on? Send it over.