A free house hacking calculator, no account needed

Something I wish I’d had when I was running deals on a spreadsheet in a van. It’s free and will stay that way.

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Before I bought my duplex, I underwrote dozens of listings by hand, and tried multiple angles of analysis (not always consistent) which meant spreadsheets over and over, trying not to fool myself. After I closed, I built the calculator on this site so you don’t have to do that. It’s free, and it doesn’t make you hand over your email to see your own numbers. That last part matters. A lot of calculators in this space make you create an account or hand over your email before they’ll show you your own numbers. The core math should be free and open, and that’s how I built this one.

What it does

Plug in a real listing and the expected rents, and it returns the numbers that actually decide whether a house hack works:

• Effective housing cost, what you’ll pay to live there after tenants chip in. The single most important number for a house hacker.
• Cash flow, what the property does on its own, including after you move out.
• Cap rate, the property’s return independent of your financing.
• Cash-on-cash return, what your invested cash earns.

It handles the FHA reality too, low down payment, MIP, the works, so the output reflects how a real owner-occupied deal actually pencils out, not a fantasy version.

How to read it

Two habits will keep your numbers real:

• Model maintenance high. Set your repair reserve to 12–15% on older properties, not 5%. My 1925 duplex surfaced a $20,000 boiler in year one, the calculators that assume 5% would’ve told me a comforting lie.
• Don’t trust a great-looking result. If your projected cash flow looks much better than a comparable real deal, you’re probably missing an expense line. The calculator is only as good as your inputs.

Why it’s free

I’m an accountant who got obsessed with the 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 it helps you avoid a bad deal or find a good one, that’s the whole return I’m after. If you later decide you want the full step-by-step version, there’s 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. If you want to model a deal over a longer hold, the projection tool runs it year-by-year, and the roadmap tells you whether your finances are ready to start. Open the calculator and run a real listing. No signup. Just the math.

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

New to the idea? Here’s house hacking explained in plain English.