CPI and Forex: How Inflation Data Moves Currencies

What is CPI and why does it matter in forex?

CPI stands for consumer price index. It measures the price of a typical basket of goods and services that households buy, compared with a month or a year earlier, so it is the main gauge of inflation. It matters in forex because inflation guides central-bank interest rates, and interest-rate expectations are one of the strongest drivers of currencies.

The basket holds thousands of items, from food and rent to fuel. If it cost $100 a year ago and costs $103 today, annual inflation is 3%.

Headline CPI vs core CPI

• Headline CPI: the whole basket, and the number closest to what households feel.
• Core CPI: the same basket with food and energy taken out.

Food and energy prices jump around with the weather, wars and oil supply, and those swings often reverse. Core gives a steadier picture of the trend. When the two disagree, for example the headline falls because petrol got cheaper while core rises, the market usually follows core.

Month-on-month vs year-on-year

Year-on-year (y/y) compares prices with the same month a year ago. It is the figure in the news and the one compared with the central bank’s target. Month-on-month (m/m) compares prices with the previous month, so it is the freshest reading.

The yearly figure can fall simply because a big monthly rise from a year ago drops out of the 12-month window, even if prices are rising quickly now. That is why traders watch the monthly core figure most closely. Small differences matter: 0.2% a month for a year is about 2.4%, while 0.4% a month is nearly 5%. A miss of one tenth of a percentage point can move the dollar sharply.

Who publishes CPI and when?

In the United States, the Bureau of Labor Statistics publishes CPI once a month, usually around the middle of the month, at 8:30 a.m. New York time. That is 13:30 UTC in winter and 12:30 UTC during US daylight saving time, so 9:30 p.m. or 8:30 p.m. in Singapore and Kuala Lumpur.

Other countries work in a similar way: Eurostat for the euro area, the Office for National Statistics in the UK, Statistics Canada and Japan’s Statistics Bureau all publish monthly figures. Dates and forecasts are listed on an economic calendar.

How does inflation affect a currency?

Inflation means money buys less, so high inflation should be bad for a currency. Yet when US CPI comes in higher than expected, the dollar usually jumps. Both are true, over different time frames.

• Over years: a country with higher inflation than its trading partners tends to see its currency fall. Its exports become expensive and each unit of the currency buys less.
• Over minutes, days and weeks: traders ask one question: what will the central bank do? A trusted central bank fights inflation by raising interest rates or keeping them high for longer. Higher rates mean better returns on deposits and bonds in that currency, which pulls in money from abroad. So a “hot” CPI number, one above the forecast, lifts the currency, not because inflation is good, but because of the response traders expect.

The key word is trusted. If investors doubt that the central bank will act, higher inflation just means the currency is losing value with no reward for holding it, and it falls. What counts is the real interest rate: the interest rate minus inflation. A currency paying 5% with 3% inflation offers a real return of 2%. One paying 10% with 15% inflation offers minus 5%, and investors leave.

Why the surprise matters more than the number

Before each release, economists publish forecasts, and their average, the consensus, is already built into prices. The market moves on the gap between the actual figure and the consensus. The chain runs like this:

• CPI comes in above or below the forecast.
• Traders change their view of future interest rates.
• Government bond yields, the interest return on bonds, move within seconds.
• The currency follows yields.

Take a clearly hypothetical release. The consensus is 3.0% y/y for the headline and +0.3% m/m for core. The actual figures are 2.9% and +0.5%. The headline looks like good news, but core is two tenths above forecast, which is a big miss. Traders now expect higher rates for longer, yields jump and the dollar ends the hour sharply higher. Now flip it: a 3.0% figure that exactly matches the forecast might move nothing at all.

The Federal Reserve, the European Central Bank, the Bank of England and the Bank of Japan all aim for inflation of 2%. The further inflation sits above that, the more each upside surprise worries the market. Our guide to FOMC meetings shows how the Fed turns the data into decisions.

Related inflation measures: PCE, PPI and wages

• PCE price index: personal consumption expenditures, published by the US Bureau of Economic Analysis near the end of the month. It is the Fed’s preferred gauge, and its 2% target is measured with it. It usually moves markets less than CPI, because it comes later and analysts can estimate it fairly well in advance.
• PPI: the producer price index measures the prices businesses receive. It hints at cost pressure that may reach consumers later.
• Wage growth: fast-rising wages push companies to raise prices and give workers more to spend. In the US, average hourly earnings arrive with the non-farm payrolls report.

What happens in the first minutes after CPI?

The general mechanics of news releases are in our guide to trading the news. The typical CPI sequence:

• Just before: the banks that supply prices pull back their quotes. The spread, the gap between the buy and sell price, widens on dollar pairs and gold.
• The spike: at 8:30 a.m. machines trade on the numbers within milliseconds. A major pair can jump tens of pips (a pip is the smallest standard price step, 0.0001 on most pairs) in seconds.
• The second look: over the next 5 to 30 minutes, people read the details. The spike may extend, stall or fully reverse.
• The follow-through: a real surprise that changes the rate outlook often sets the direction for the rest of the day. A small one tends to fade.

Three ways to handle a CPI release

• Stay flat: close or avoid dollar and gold positions from about 15 minutes before the release until spreads return to normal. Risk note: any longer-term trades you keep open still need stop-losses, the orders that close a losing trade, outside the likely spike.
• Reduce size: cut the position and widen the stop so that less money is at risk. Suppose on a $5,000 account you normally risk 1% ($50) with a 25-pip stop on EUR/USD, which is 0.20 lots (20,000 units) at about $2 a pip. For CPI you halve the risk to $25 and widen the stop to 50 pips: 25 ÷ 50 = $0.50 a pip, or 0.05 lots, a quarter of your usual size. The position size calculator does this sum for any pair. Risk note: a stop can be filled worse than its level, so the loss can still exceed the plan.
• Trade after the dust settles: wait 15 to 30 minutes, let spreads normalise and see which direction survived the second look. Then trade in that direction with a stop beyond a clear level. Risk note: you give up the first move, and later reversals still happen.

Which pairs react most to US CPI?

• USD/JPY: often the most sensitive major pair, because USD/JPY tracks US bond yields closely.
• EUR/USD and GBP/USD: both react strongly. EUR/USD is the most heavily traded pair, so its spread usually recovers fastest.
• Gold: XAU/USD pays no interest. Many people see gold as protection against inflation, yet on CPI day a hot number usually hits it, because of what that number means for rates.
• AUD/USD and NZD/USD: these react twice, through the dollar and through the risk mood, since a hot CPI often knocks share markets too.

How wide spreads get on days like this differs from broker to broker, which is worth checking in an independent broker comparison.

Understanding CPI tells you why the market moved. It cannot tell you the number in advance. Forex and CFDs carry a high risk of loss, and that risk is higher than usual in the minutes around major data. Only risk money you can afford to lose.