Most new investors overcomplicate house hacking math. Here's the entire framework in one formula:

Net Housing Cost = PITI + Maintenance Reserve + Vacancy Reserve − Rental Income (non-owner units)

3 possible outcomes:

• Net Housing Cost ≤ $0 → you live for free (or get paid to live there)

• Net Housing Cost is well below local market rent → you're subsidized, still a great deal

• Net Housing Cost ≈ market rent or higher → pass, the deal doesn't earn its keep

The stress test that separates good deals from lucky ones:

Recalculate with rents 10% below your estimate and vacancy at 10%. If the deal still clears "subsidized" under those conditions, it's resilient — not just lucky timing.

A lot of people skip the stress test and get burned when a tenant leaves or rents soften. Run your numbers twice: once optimistic, once conservative. If both pass, you've got a real deal.

Happy to break down a specific property's numbers in the comments if you're working through your first one.