Not the mortgage payment — the part you never get back. Interest, property tax, insurance, maintenance. Rent is 100% money gone; a mortgage payment isn't. This compares the two honestly, and it handles buying an existing house or buying a lot and building on it.
This is the fair comparison. Rent is entirely gone. A mortgage payment isn't — the principal is savings, moving from your bank account into your house. Strip that out and here is what each option actually costs you.
What actually leaves your account — including the principal, which you keep.
Same dollars, different amounts of house. This is the part a monthly-payment comparison hides.
Equity you'd build by owning, against the cash you'd have if you kept renting and invested the difference.
Most rent-versus-buy calculators compare a rent check to a mortgage payment. That comparison is wrong in both directions at once. It overstates the cost of owning by counting principal — which is savings, not an expense — and it understates it by ignoring property tax, insurance, and maintenance, which on a Middle Tennessee house can add six or eight hundred dollars a month.
So this tool separates the two questions. First: what does each option actually cost you, counting only money that doesn't come back — rent and renter's insurance on one side; mortgage interest, property tax, homeowner's insurance, HOA, maintenance and the return your down payment gives up on the other. Second: what leaves your bank account each month, which is the number that decides whether you can sleep at night.
Then it shows what you're getting for it. If you're renting 1,600 square feet and building 2,600, comparing the payments alone is not a fair fight — you're buying a different thing. The cost per square foot makes that visible.
Tennessee assesses residential property at 25% of appraised value, then applies a rate per $100 of that assessed value. A $500,000 house is assessed at $125,000; at Davidson County's Urban Services District rate of $2.814, that's $3,517 a year. The same house in unincorporated Wilson County at $1.1657 is $1,457 — a difference of about $170 a month for identical houses. That gap is why the county selector matters more than most people expect.
If you build for less than the finished home is worth, that difference is equity you own the day you move in — it isn't a return you have to wait for. The calculator shows it separately, because it's the single biggest advantage available to someone who can build at cost, and it doesn't show up anywhere in a monthly payment comparison.