The affordability calculator
What can a household afford here, and when does buying beat renting?
Pick a metro, type an income, choose a down payment, a rate and a horizon. The calculator answers with the payment on the median home as a share of that income, the price the income can carry at the 30% line, the share of households in the metro that can afford the median home, and the rent or buy breakeven with the interval the metro's own history gives it. The rate defaults to the latest Freddie Mac week (7.32%, week of 2026-10-22); prices rest on 2026Q2 and incomes on the 2024 census release.
The answers come from the live API. Its instance stops when idle and starts again on the first request; the page asks twice, and if it is still starting it answers from a session recorded against the live API and says so.
Rent or buy
Renter wealth less owner equity by year under the metro's median appreciation and rent growth; the interval comes from its own history
Source: the live API over the committed calculator marts.
Save this check through the API. The log stores the metro code, the income rounded to the nearest thousand, the down payment share, the rate and the horizon, nothing else, and scores the check when the next quarter of prices and rates publishes.
The rent or buy decision across metros
Buying beats renting only after 10.0 years in the typical metro (interval 1.0 years to beyond 30 years), and one point of rate moves the breakeven by +4.5 years. Longest to break even among the largest metros: Boston-Cambridge-Newton 21 years; Chicago-Naperville-Elgin 20 years; San Francisco-Oakland-Fremont 18 years.
Renter wealth less owner equity by horizon for the largest metro at 6.72%, with the breakeven marked and its interval across metros
dollars, positive means renting is ahead
real:fhfa+acs+pmms
What the housing economist would push back on
A payment is not the whole cost of owning: the cost model adds taxes, insurance, maintenance and the costs of buying and selling, but not the roof that fails in year four, and it credits the renter with a return the renter has to earn. The paths are drawn from the metro's own past, which includes a decade nobody expects to repeat, and the interval is the spread of those paths, not a forecast. The down payment years assume a renter who saves a tenth of income with no help and no return, which is the simplest honest reading of the question. The 30% line is doing work: at 28%, the sensitivity line, the median household can afford the median home in 191 of the 382 metros rather than 221, and the majority reading goes with the line.