New single-family homes in Austin list at a median of $218 per square foot. Resale homes in the same Realtor.com search ask $304. On those two numbers alone, a new build is 28% cheaper than a used one, which is not what most buyers walking through a model home would expect.

I wanted to know whether that holds up, so I pulled new construction and resale listings for nine US metros with Python and compared them three ways: by city, by size band and inside the same ZIP code. The short version: the city numbers lie, and the reason they lie is the most useful thing in the data.

The data

Everything here comes from the Realtor.com Data API , which returns Realtor.com search results as JSON.…