In the retail currency exchange market, different buying and selling rates will be quoted by money dealers. Most trades are to or from the local currency. The buying rate is the rate at which money dealers will buy foreign currency, and the selling rate is the rate at which they will sell that currency. The quoted rates will incorporate an allowance for a dealer's margin (or profit) in trading, or else the margin may be recovered in the form of a commission or in some other way. Different rates may also be quoted for cash, a documentary transaction or for electronic transfers. The higher rate on documentary transactions has been justified as compensating for the additional time and cost of clearing the document. On the other hand, cash is available for resale immediately, but incurs security, storage, and transportation costs, and the cost of tying up capital in a stock of banknotes (bills).
There is a market convention that rules the notation used to communicate the fixed and variable currencies in a quotation. For example, in a conversion from EUR to AUD, EUR is the fixed currency, AUD is the variable currency and the exchange rate indicates how many Australian dollars would be paid or received for 1 euro.
In some areas of Europe and in the retail market in the United Kingdom, EUR and GBP are reversed so that GBP is quoted as the fixed currency to the euro. In order to determine which is the fixed currency when neither currency is on the above list (i.e. both are "other"), market convention is to use the fixed currency which gives an exchange rate greater than 1.000. This reduces rounding issues and the need to use excessive numbers of decimal places. There are some exceptions to this rule: for example, the Japanese often quote their currency as the base to other currencies.
Countries are free to choose which type of exchange rate regime they will apply to their currency. The main types of exchange rate regimes are: free-floating, pegged (fixed), or a hybrid.
Still, some governments strive to keep their currency within a narrow range. As a result, currencies become over-valued or under-valued, leading to excessive trade deficits or surpluses.
A market-based exchange rate will change whenever the values of either of the two component currencies change. A currency becomes more valuable whenever demand for it is greater than the available supply. It will become less valuable whenever demand is less than available supply (this does not mean people no longer want money, it just means they prefer holding their wealth in some other form, possibly another currency).
The rate of change of the real exchange rate over time for the euro versus the dollar equals the rate of appreciation of the euro (the positive or negative percentage rate of change of the dollars-per-euro exchange rate) plus the inflation rate of the euro minus the inflation rate of the dollar.
UIRP showed no proof of working after the 1990s. Contrary to the theory, currencies with high interest rates characteristically appreciated rather than depreciated on the reward of the containment of inflation and a higher-yielding currency.
The balance of payments model holds that foreign exchange rates are at an equilibrium level if they produce a stable Current account (balance of payments)current account balance. A nation with a trade deficit will experience a reduction in its foreign exchange reserves, which ultimately lowers (depreciates) the value of its currency. A cheaper (undervalued) currency renders the nation's goods (exports) more affordable in the global market while making imports more expensive. After an intermediate period, imports will be forced down and exports to rise, thus stabilizing the trade balance and bring the currency towards equilibrium.
In general, exporters of goods and services will prefer a lower value for their currencies, while importers will prefer a higher value.