Central Bank Intervention

Currency intervention happens when a central bank or finance ministry buys or sells currencies in the foreign exchange market to influence the exchange rate. A country whose currency has fallen too fast may sell foreign reserves to buy its own currency; one whose currency is too strong may sell its own currency to weaken it. Intervention can cause some of the sharpest moves in forex, and the threat of it shapes how traders position around key levels.

Types of intervention#

Famous examples#

• Plaza Accord (1985): the US, Japan, West Germany, France and the UK agreed to weaken the dollar, which fell sharply over the next two years.
• Black Wednesday (1992): the Bank of England raised rates and bought pounds to keep sterling in the European Exchange Rate Mechanism but failed; the UK left the mechanism, and speculators including George Soros profited. See Famous Trades in History.
• Swiss franc cap (2011 to 2015): the Swiss National Bank capped the franc at 1.20 per euro, buying huge amounts of euros. On 15 January 2015 it abandoned the cap without warning, and the franc surged around 30% within minutes.
• Japan (2022 and 2024): Japan's Ministry of Finance bought yen to slow its fall, including about ¥9.2 trillion in 2022 and further large purchases in 2024, according to official data. See The ECB and the BOJ.

How intervention affects prices#

Does intervention work?#

Evidence suggests:

• Short term effects can be large, especially when intervention is a surprise or coordinated.
• Long term effects depend on fundamentals. If interest rate differentials and economic conditions keep pushing the other way, intervention often only slows the trend. See Interest Rate Differentials.
• Defending a weak currency is limited by reserves; weakening a strong currency is limited only by willingness to create money, which is why the Swiss cap lasted over three years.

Warning signs#

• Rapid, one directional moves that officials describe as "excessive" or "speculative".
• Escalating verbal warnings from finance ministers and central bankers.
• Rate checks: reports that a central bank has asked dealers for prices, often a final warning.
• Round number levels that officials appear to care about.

How traders manage intervention risk#

1. Reduce leverage when trading against a currency that authorities are defending. See Leverage and Margin in Forex.
2. Expect gaps: stops may fill far from their levels. See Slippage.
3. Avoid crowded positions near levels that have triggered action before.
4. Watch official statements and data releases on intervention amounts.
5. Remember the Swiss lesson: a peg can end suddenly, and brokers may fail. Prefer well regulated brokers with negative balance protection.

Frequently asked questions#

What is currency intervention?#

When a central bank or government buys or sells currencies in the market to influence its exchange rate.

Why did the Swiss franc jump in 2015?#

The Swiss National Bank removed its cap of 1.20 francs per euro without warning, and the franc surged about 30% against the euro within minutes.

Does central bank intervention work?#

It can cause large short term moves, but lasting effects usually require supportive fundamentals, such as changes in interest rates.

Next, learn about the benchmark rates set each day in FX Fixings: London and Tokyo.