US inflation calculator — cumulative CPI inflation between any two years, e.g. what $100 in 1990 is worth today (?from=1990&to=2026&amount=100). Returns cumulative inflation % and the inflation-adjusted value as JSON, from official CPI data via FRED (Federal Reserve). Use for: purchasing power comparison, real vs nominal value, historical price adjustment, cost-of-living calculation. $0.003 USDC per call.