Buy-path cost = down payment + 48 months of (mortgage + tax + insurance + maintenance) + opportunity cost on the down payment − 48 months of rent collected (after vacancy) − (sale price − remaining mortgage balance − 6% selling cost).

Opportunity cost: Your down payment could be earning a return elsewhere. We charge its compounded opportunity cost over the 4-year hold (default 5%/yr) so recovered equity isn’t credited for free.

Sale price at year 4: Assumes 3% annual appreciation by default; you can see what this city’s actual 5-year CAGR was by visiting any linked ZIP page.

Insurance: 0.5% of home value/year. Maintenance: 1% of home value/year. These are industry rules of thumb.

Rent collected: (bedrooms − 1) × rent per roommate × months occupied × (1 − vacancy). One bedroom is assumed for your kid.

Apples-to-apples: Dorm room & board includes food, but the buy path is housing-only, so we subtract the food/board portion from the dorm cost before comparing.

This is a simplified analysis. It does not account for income tax on rental, mortgage interest deduction, HOA fees, or your kid not being a great landlord. It’s a starting point — always consult a CPA before making a decision this size.