Whether Core Inflation Beat Expectations Depends on the Yardstick
September's consumer price index came in above Bloomberg's year-over-year consensus, making it an upside surprise on that measure. Switch to month-over-month figures, though, and the picture splits: because of rounding, core CPI did not exceed consensus in September, while headline did. Same release, same month, two answers to the question of whether inflation surprised.
The part that travels is what happened next: nowcasts of inflation picked up for both headline and core as a consequence of the release. A miss on one chart gets read as information about where prices are heading, not just where they have been — which is why the choice between an annual and a monthly yardstick is not a technicality.
AI-generated discussion · Different perspectives
A "surprise" is a gap between a number and a survey of forecasters, not a description of prices. Core inflation still rose in September; it just didn't beat the consensus on the monthly measure.
Fair, but the release still moved expectations: nowcasts for headline and core both ticked up afterward. Markets and policymakers respond to the surprise, not to the rounding.
The annual figure is about the trend a reading sits in, the monthly figure about the reading itself. Both are true, and which one counts depends on what you are trying to learn.