Inflation and CPI explained: why one number moves the whole market
What the Consumer Price Index measures, headline vs core, why a hot or cool CPI moves futures, what a CPI morning looks like and a plan for trading it.
Once a month, at 8:30 in the morning New York time, a single number can move the Nasdaq more than an entire normal day. That number is the Consumer Price Index, or CPI. Here's what it measures, why the market cares, and how to handle CPI mornings as a day trader.
What CPI measures
CPI tracks the price of a basket of everyday things people buy: food, rent, gas, clothes, medical care, travel. When the basket costs more than a year ago, that's inflation. The report comes from the U.S. Bureau of Labor Statistics, usually around the middle of each month.
- Headline CPI: everything in the basket.
- Core CPI: everything except food and energy, which jump around a lot. The Fed and the market often watch core more closely.
- Month-over-month and year-over-year: the change from last month, and from the same month last year. Both are shown, and both can move the market.
Why the market cares
Inflation decides what the Fed does next. Hotter-than-expected inflation means rates may stay high for longer, which is usually bad for stocks, and especially for the Nasdaq. Cooler-than-expected inflation means rate cuts could come sooner, which stocks usually like. See the Fed and interest rates.
| CPI comes in… | What it suggests | Typical first reaction |
|---|---|---|
| Above the forecast ("hot") | Rates stay higher for longer | Index futures fall, yields and the dollar rise |
| In line | Nothing new | A short, choppy move, then the day goes on |
| Below the forecast ("cool") | Rate cuts may come sooner | Index futures rise, yields and the dollar fall |
“Typical” is the important word. Sometimes the first move reverses within minutes as traders read the details. That's exactly why the first minutes are so dangerous.
What a CPI morning looks like
- Before 8:30 a.m. ET: futures are often quiet as traders wait. Liquidity thins out.
- 8:30:00: the number comes out. Prices can jump many points in a second, and fills can slip far from your order price. See bid, ask, spread and slippage.
- 8:30 to 9:30: the market digests the number before the stock market opens at 9:30, which brings a second wave of volume.
A plan for CPI days
- Know the date. Check the economic calendar the week before, and write “CPI 8:30” in your Morning prep plan.
- Be flat at 8:30. Holding a position through the release is a coin flip with a slippage tax.
- Let the first move settle. Many traders wait until the regular open at 9:30, or for the first 15-minute range to form.
- Trade smaller. Ranges are bigger on CPI days, so the same stop distance in points means more dollars at risk. Use the position size calculator.
- Check your firm's rules. Some prop firms restrict trading in the minutes around major data. See news trading on a prop account.
Next in this series
Next: the jobs report, the other big monthly number. To see whether your news days cost you money, drop your trades into the free trading report card.
This article is for education only and isn't financial advice. Release times can change; check the official calendar. Trading futures involves substantial risk of loss.