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CPI Explained, Why Inflation Data Moves Currencies

The Consumer Price Index (CPI) measures how much prices for a basket of goods and services have changed. It's one of the most watched economic releases because it shapes expectations about interest rates.

Why traders care: central banks aim to keep inflation near a target. If inflation runs higher than expected, markets may expect higher interest rates, which can strengthen a currency. If inflation is lower than expected, rate cut expectations may rise, which can weaken it.

What to look at:

- Headline CPI: includes all items, such as food and energy
- Core CPI: excludes volatile food and energy prices, giving a cleaner trend
- Month-over-month and year-over-year changes: both matter
- The surprise: the difference between the actual number and the forecast

How the market usually reacts:

1. Before the release, price may drift or consolidate as traders wait.
2. At the release, volatility spikes, with sharp moves in both directions.
3. After the first reaction, price often finds a direction as traders digest details.

How to handle it:

- Check the calendar for release times
- Avoid new positions in the minutes before the release
- Wait for the dust to settle, then use structure and liquidity to find setups
- Keep stops wider than usual, and reduce size

Remember: the market reacts to the surprise relative to expectations, not simply to the number itself.

Learn the schedule, respect the volatility, and let others gamble on the first spike.

Worked example of how I'd read a CPI release. Forecast is 3.1%, it prints 3.4%. Hotter than expected usually supports the currency because it raises the odds of rates staying high. But if core CPI comes in soft at the same time, the first spike often fades. Read the headline and core together before you do anything.

Fairman wrote: Month-over-month and year-over-year changes: both matter

For US CPI the monthly core figure is usually the one that moves price first, and it's published rounded to one decimal. That rounding hides a lot: a 0.3 can be anything from 0.25 to 0.34, and analysts often post the unrounded figure within a minute or two. A "hot" 0.3 that turns out to be 0.25 can reverse the first spike quickly, which is one reason the initial move on CPI is so unreliable.

The year-over-year figure also has base effects worth checking a day ahead. If a big monthly jump drops out of the twelve-month window, the annual rate can fall even when this month's number is firm, and headlines will report it as inflation cooling.

A mistake I see around CPI is people treating the monthly change and the annual rate like they're interchangeable. Sometimes one beats and the other misses, and the market picks one to care about. Usually it's whatever the central bank has been talking about lately. Base effects cause a lot of this. If prices jumped a year ago, the annual rate can fall even when this month's increase is high, which looks like good news on the headline but isn't. For US CPI, core month on month has often been the number that matters most. Read all four figures before forming a view.

For anyone trading it live, spreads usually widen in the seconds before the release and can stay wide for a minute or two after. Even if you read the number perfectly, entering in that window is expensive. I'd rather wait for the first 5 minute candle to close. US CPI comes at 8:30 New York, so 1:30pm Lagos in summer and 2:30pm in winter. My routine is to be flat or have stops well away from price by 1:25pm, watch the first candle, and then look for a setup that agrees with the number, with the spread back to normal. Missing the first 20 pips is fine.