In modern monetary policy, a devaluation is an official lowering of the value of a country's currency within a fixed exchange rate system, by which the monetary authority formally sets a new fixed rate with respect to a foreign reference currency or currency basket. In contrast, a depreciation is a decrease in a currency's value (relative to other major currency benchmarks) due to market forces under a floating exchange rate, not government or central bank policy actions.
A central bank maintains a fixed value of its currency by standing ready to buy or sell foreign currency with its own currency at a stated rate; a devaluation is a change in this stated rate that renders the foreign currency more expensive in terms of the home currency.
The opposite of devaluation, a change in the fixed rate making the foreign currency less expensive, is called a revaluation.
Related but distinct concepts include inflation, which is a market-determined decline in the value of the currency in terms of goods and services (related to its purchasing power). Altering the face value of a currency without reducing its exchange rate is a redenomination, not a devaluation or revaluation.
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Devaluation is most often used in a situation where a currency has a defined value relative to the baseline. Historically, early currencies were typically coins struck from gold or silver by an issuing authority which certified the weight and purity of the precious metal. A government in need of money and short on precious metals might decrease the weight or purity of the coins without any announcement, or else decree that the new coins have equal value to the old, thus devaluing the currency.
Later, with the issuing of paper currency as opposed to coins, governments decreed them to be redeemable for gold or silver (a gold standard). Again, a government short on gold or silver might devalue by decreeing a reduction in the currency's redemption value, reducing the value of everyone's holdings.
In modern economies
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At the outbreak of World War II, in order to stabilise sterling, the pound was pegged to the US dollar at the rate of $4.03 with exchange controls restricting convertibility volumes. This rate was confirmed by the Bretton Woods agreements of 1944.
After the war ended, US lend-lease funding, which had helped finance the UK’s high level of wartime expenditure, was abruptly ended and further US loans were conditional upon progress towards sterling becoming fully convertible into US dollars thereby aiding US trade. In July 1947, sterling became convertible but the resultant drain on the UK’s reserves of US dollars was such that 7 weeks later, convertibility was suspended, rationing tightened and expenditure cuts made. The exchange rate reverted to its pre-convertibility level, a devaluation being avoided by the new Chancellor the Exchequer Stafford Cripps choking off consumption by increasing taxes in 1947.
By 1949, in part due to a dock strike, the pressure on UK reserves supporting the fixed exchange rate mounted again at a time when Cripps was seriously ill and recuperating in Switzerland. Prime Minister Clement Attlee delegated a decision on how to respond to 3 young ministers, whose jobs included economic portfolios, namely Hugh Gaitskell, Harold Wilson and Douglas Jay, who collectively recommended devaluation. Wilson was despatched with a letter from Attlee to tell Cripps of their decision, expecting that the Chancellor would object, which he did not. On 18 September 1949 the exchange rate was reduced from $4.03 to $2.80 and a series of supporting public expenditure cuts imposed soon afterwards.
When the Labour Government of Prime Minister Harold Wilson came to power in 1964, the new administration inherited an economy in a more parlous state than expected with the estimated balance of payments deficit for the year amounting to £800 million, twice as high as Wilson had predicted during the election campaign. Wilson was opposed to devaluation, in part due to the bad memories of the 1949 devaluation and its negative impact on the Attlee government, but also due to the fact that he had repeatedly asserted that Labour was not the party of devaluation. Devaluation was avoided by a combination of tariffs and raising $3bn from foreign central banks. It has been suggested that, following the crisis, Wilson was so keen to avoid further pressure on sterling that in 1965 he publicly announced the British government would not use force to prevent Rhodesia declaring independence, thereby removing the one major uncertainty holding back the Rhodesian government from doing just that.
By 1966, pressure on sterling was intensifying, due in part to the seamen's strike, and the case for devaluation being articulated in the higher echelons of government, not least by the deputy prime minister George Brown. Wilson resisted and eventually pushed through a series of deflationary measures in lieu of devaluation including a 6 month wage freeze. As a consequence Brown resigned but then changed his mind and remained in the government.
After a brief period in which the deflationary measures relieved sterling, pressure mounted again in 1967 as a consequence of the Six-Day War, the Arab oil embargo and a dock strike. After failing to secure a bail-out from the Americans or the French, a devaluation in the parity rate of £1 from $2.80 to $2.40 was announced at 9:30 p.m. on Saturday 18 November 1967.  In a broadcast to the nation the following day, Wilson said, “Devaluation does not mean that the value of the pound in the pocket in the hands of the…British housewife…is cut correspondingly. It does not mean that the pound in the pocket is worth 14% less to us now than it was.” This wording is often misquoted as “the pound in your pocket has not been devalued.”
China devalued its currency twice within two days by 1.9% and 1% in July 2015. India devalued its currency by 35% in 1977.
Fixed exchange rates are usually maintained by a combination of legally enforced capital controls and the central bank standing ready to purchase or sell domestic currency in exchange for foreign currency. Under fixed exchange rates, persistent capital outflows or trade deficits will involve the central bank using its foreign exchange reserves to buy domestic currency, to prop up demand for the domestic currency and thus to prop up its value. However, this activity is limited by the amount of foreign currency reserves the central bank owns; the prospect of running out of these reserves and having to abandon this process may lead a central bank to devalue its currency in order to stop the foreign currency outflows.
In an open market, the perception that a devaluation is imminent may lead speculators to sell the currency in exchange for the country's foreign reserves, increasing pressure on the issuing country to make an actual devaluation. When speculators buy out all of the foreign reserves, a balance of payments crisis occurs. Economists Paul Krugman and Maurice Obstfeld present a theoretical model in which they state that the balance of payments crisis occurs when the real exchange rate (exchange rate adjusted for relative price differences between countries) is equal to the nominal exchange rate (the stated rate). In practice, the onset of crisis has typically occurred after the real exchange rate has depreciated below the nominal rate. The reason for this is that speculators do not have perfect information; they sometimes find out that a country is low on foreign reserves well after the real exchange rate has fallen. In these circumstances, the currency value will fall very far very rapidly. This is what occurred during the 1994 economic crisis in Mexico.
After a devaluation, the new lower value of the domestic currency will make it less expensive for foreign consumers to obtain local currency with which to buy locally produced export goods, so more exports will be sold, helping domestic businesses. Further, the new exchange rate will make it more expensive for local consumers to obtain foreign currency with which to import foreign goods, hurting domestic consumers and causing less to be imported. The combined effect will be to reduce or eliminate the previous net outflow of foreign currency reserves from the central bank, so if the devaluation has been to a great enough extent the new exchange rate will be maintainable without foreign currency reserves being depleted any further.
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