Cost of Living the marginal buyer's inflation — own-home payment priced at today's rate

Identical to the headline macrogauge in every component but one: owned shelter. CPI — and our gauge — prices the home you already own by rental equivalence (what it would rent for): the cost of keeping the life you have. Cost of Living instead prices the marginal buyer's payment — a home valued at 0.80× the Zillow Home Value Index, financed at the daily 30-year mortgage rate (Mortgage News Daily, Freddie Mac PMMS fallback): the cost of buying that life today. Everything else — food, energy, vehicles, services — rides the same live data as the gauge. Why it runs hotter when rates rise: the buyer's payment compounds two moving parts, the price of the house and the price of the money, so a rate jump raises the payment even while home prices sit still — and rental-equivalence CPI barely stirs. The divergence is the signal, not an error: vs official CPI it correlates 0.9383 with a mean absolute gap of 3.29pp (2018-01..2026-08). See methodology for validation stats.