CPI inflation

A basket of consumer prices

The Consumer Price Index is a weighted basket of prices for goods and services that urban US consumers buy. The Bureau of Labor Statistics surveys roughly 80,000 prices each month across categories — food, energy, housing, transportation, medical care, recreation, education — and aggregates them into a single index. The most common headline series is CPIAUCSL, the all-items index for all urban consumers, seasonally adjusted.

The index level itself (e.g., 310.0 in some month) is not meaningful in isolation. What matters is the rate of change. By convention, the headline inflation rate is the year-over-year percent change in CPIAUCSL — today's index versus the same month one year ago.

Twelve months smooths the noise

Month-over-month CPI prints are noisy. Energy and food can move several percent in a single month for reasons that have nothing to do with the trend. Seasonal adjustment helps, but a single print can still mislead.

The year-over-year change — the read the engine consumes — smooths most of that noise by construction. It compares the latest index to a value twelve months earlier, so seasonal effects mostly cancel out, and one-month spikes are averaged against eleven other months of context. It also matches how the FOMC, the bond market, and most financial commentary actually talk about inflation.

Two tightening cycles, two stories

The reason CPI matters to a market signal is not because high inflation directly causes selloffs. It is because high inflation changes what Fed policy means. Consider two superficially similar cycles:

Same destination on the rate. Wildly different stress on the system. The variable that explains the difference is the inflation context the Fed was reacting to.

One source of pressure in the bear overlay

CPI is part of the bear overlay, alongside fed funds change and unemployment. The engine does not read inflation in isolation — it reads it in combination with whether the Fed is responding. The combination matters because the two readings carry opposite implications without each other: high inflation with a cutting Fed (e.g., the depths of the 2008 crisis) describes a very different environment from high inflation with a tightening Fed (e.g., 2022). The engine treats inflation as one source of macro pressure only when both legs — elevated YoY inflation and an actively tightening Fed — are present at the same time.

Inside the bear gate, this combined condition counts as one of the macro-pressure sources that can support bear regime entry.

The specific inflation level required and the way the “actively tightening” condition is measured are part of the production rule and are not published. The educational point is the conjunction: an inflation print is read in the context of policy, not as a standalone gate.

CPI is one of four macro anchors. VIX percentile reads volatility. Fed funds change reads policy. Unemployment reads labor. None decides a signal alone. Together with the price-based features — drawdown depth, duration, sharpness, and dual-timeframe Williams %R — they tell the regime classifier whether the environment around a candidate reversal is the kind where the rule has historically worked.