What is measured. Two chained price indices for the goods and services wealthy US households buy, 2016 = 100, one observation per calendar year. CPI Reserve (series CPI-R) is a 44-item basket for households worth roughly $10–100m; CPI Sovereign (series CPI-RS) is a 29-item basket for $100m+ households, weighted toward carrying costs: residences, aviation, marine, staff and family office, collectibles, access and philanthropy. Both are compared with the Bureau of Labor Statistics CPI-U (all items, annual average, rebased to 2016 = 100).
Price concept. Nominal US dollars, the price actually paid (list price, published rate card, posted salary, fee schedule, median transaction price), before tax unless stated. Foreign-currency items are converted at the calendar-year average exchange rate. Where a product's capacity or specification changed, the series is quality-adjusted (for example Necker Island is priced per guest-night because the island's capacity rose from 34 to 48 guests) and the adjustment is stated in the item definition.
Aggregation. Each year-on-year link is a geometric mean of item price relatives. CPI Reserve aggregates in two stages: the unweighted geometric mean of item relatives within each category, then a weighted average of category relatives using the category weights shown below; CPI Sovereign is a single-stage weighted geometric mean using the item weights. If an item has no price in either year of a link (a series break, or a product that did not exist), it drops out of that link and weights renormalise over the remaining items. The "core" variants exclude the housing (Reserve) or residences (Sovereign) category..
Evidence grades. Every cell carries a flag. observed = a figure read on a dated page, with its URL recorded (official sites, archived copies in the Internet Archive, brokerage and auction reports, SEC filings, court filings, trade press, enthusiast forums with dated receipts). interpolated = geometric interpolation between two observed years. estimated = extrapolated beyond the last observation, back-cast with a stated model, or re-levelled to a single anchor. Estimated cells affect the level of an item but, where they are flat carries, contribute nothing to inflation. Items with fewer than three observations are marked "est." on the site.
Known limitations. Housing uses median transaction prices in thin luxury markets (Palm Beach, Aspen, the Hamptons), which are noisy year to year. Several Sovereign items come from a single data provider (Aircraft Cost Calculator, Pro Pilot, Fraser Yachts listings, HAGI, Liv-ex); their methodology changes are inherited. Where the only consistent source has a slightly different scope than the ideal definition (survey average rather than top-of-market, global rather than US), the item definition says so. The basket is a judgement, not a survey of expenditure; weights are set by the authors and are adjustable on the site.
Baskets. CPI Reserve has 44 items across housing, household staff and childcare, education, travel, food and dining, apparel and luxury goods, wellness, transport, and clubs and services (category weights 30 / 12 / 12 / 12 / 8 / 8 / 7 / 5 / 6). CPI Sovereign has 29 items across residences, aviation, marine, staff and family office, art and collectibles, access and philanthropy, experience, and pocket money (21 / 14 / 8 / 17 / 11 / 13 / 8 / 8). Item-level definitions and sources are held by the authors; corrections and dated receipts are welcome.