A currency crisis is a sudden and large fall in the value of a currency, usually accompanied by heavy selling by investors, a rapid loss of official reserves and sharp increases in interest rates as the authorities try to stop the slide. Many crises end with a government abandoning a currency peg or a fixed exchange rate it had promised to hold.
Researchers often define the event by numbers. A widely cited test by Jeffrey Frankel and Andrew Rose (1996) counts a crisis when a currency loses at least 25% against the dollar in a year and the pace of depreciation also rises by at least 10 percentage points. A currency crisis differs from a planned devaluation, which is a deliberate policy choice, and from a banking crisis or sovereign default, although the three often arrive together.
Currency crisis in plain terms
Imagine a shop that promises to swap anyone's vouchers for cash at a fixed price, forever. It keeps a cash box for the purpose. If customers start to doubt that the box holds enough, they rush to swap their vouchers first, because those who wait may be left with paper worth less. The rush itself empties the box faster.
A currency crisis works the same way at the scale of a country. The central bank is the shop, its reserves are the cash box, and investors are the customers. Once doubts spread, selling feeds on itself, and the promise that looked solid a week earlier can be dropped overnight. The currency then falls to whatever level buyers are willing to pay.
How a speculative attack unfolds
Most crises follow a recognisable sequence. Investors first notice a weakness, such as a large current account deficit, rising debt or an overvalued exchange rate. They then sell the currency and buy dollars or other safe assets, a process known as capital flight. The central bank sells its foreign exchange reserves to meet that demand and raises interest rates to make holding the currency more attractive.
If reserves run low or the high rates become politically unbearable, the authorities let the currency float or devalue it. With high capital mobility, this can happen within days. The impossible trinity explains why: a country with open capital flows cannot hold a fixed rate while also keeping monetary policy independence, so any conflict between the peg and domestic goals invites a test.
Three generations of crisis models
Economists group explanations into three broad families:
- First-generation models. Paul Krugman's 1979 model showed that a government financing persistent deficits by creating money will eventually exhaust its reserves, and that speculators will attack before that point, making the collapse predictable.
- Second-generation models. Work by Maurice Obstfeld in the 1990s described governments weighing the cost of defending a peg against unemployment or debt costs. A crisis can then be self-fulfilling: if enough investors expect devaluation, defending the rate becomes too costly.
- Third-generation models. After the 1997 Asian crisis, models focused on bank fragility, short-term foreign borrowing and currency mismatch, where a falling currency inflates the local value of foreign-currency debts and damages balance sheets.
Notable episodes
On 16 September 1992, known as Black Wednesday, the United Kingdom left the European Exchange Rate Mechanism after failing to hold sterling within its band despite raising interest rates. Italy left the mechanism the same week.
In December 1994 Mexico devalued the peso, which then collapsed. The US government and the International Monetary Fund led a rescue package of about $50 billion in early 1995.
On 2 July 1997 Thailand stopped defending the baht and floated it. The fall spread to Indonesia, South Korea, Malaysia and the Philippines, where companies and banks had borrowed heavily in dollars.
In 2018 the Turkish lira lost more than a quarter of its value against the dollar over the year, while Argentina turned to the IMF for a stand-by arrangement first approved at $50 billion in June 2018, as the Argentine peso slid. Turkey's fall was driven by high inflation, large dollar debts held by companies and doubts over central bank independence, a mix that third-generation models describe well.
Prevention and policy responses
Countries use several tools to reduce the risk or contain the damage. Large reserve buffers became common across Asia after 1997. Some governments apply capital controls or other measures on short-term flows. Others move to floating exchange rates so that pressure is absorbed gradually by the price rather than all at once by reserves. International support comes from IMF lending and from bilateral or regional arrangements such as swap lines, which address dollar funding shortages directly.
Responses remain contested. Raising interest rates to defend a currency can deepen a recession, IMF programmes have been criticised for harsh conditions, and floating does not remove the danger for economies that owe large sums in foreign currency.