CPI (released mid-month at 8:30 AM ET) is the most closely watched inflation gauge by markets. Impact mechanism: Hot CPI (Core MoM ≥0.4%) → 'higher for longer' rate expectations → 10-year yield jumps 10-20bp → equity P/E compression, especially for long-duration assets (tech, growth stocks). Cool CPI (Core MoM ≤0.1%) → rate cut hopes rally → yields fall → growth stocks and bonds surge. Key details: (1) Core CPI (ex food & energy) moves markets more than headline. (2) The Shelter component (~36% of CPI) is lagging — focus on 'Supercore' (core services ex-shelter) for the true inflation trend. (3) The round-to-one-decimal trick: a 0.247% MoM rounds to 0.2% (benign) while 0.251% rounds to 0.3% (hot) — tiny differences cause outsized reactions. (4) Year-over-year base effects can distort the reading — always check MoM and 3-month annualized. (5) CPI surprises of ≥0.1% vs. consensus typically move SPX by 1-2% on the day.