Exchange rates determine how much one currency is worth in terms of another. Understanding how rates work helps you build better financial applications and make informed decisions about when to convert currencies.
What Determines Exchange Rates
Exchange rates are primarily driven by supply and demand in the forex market. Factors include interest rate differentials between countries, inflation rates, political stability, economic performance, and trade balances. Central bank policies and interventions also play significant roles.
Bid, Ask, and Mid-Market Rates
The bid rate is what buyers pay; the ask rate is what sellers receive. The difference is the spread—profit for currency exchangers. The mid-market rate (average of bid and ask) represents the "true" exchange rate. Most APIs provide mid-market rates; actual transactions include spreads.
Base and Quote Currencies
In a currency pair like EUR/USD = 1.10, EUR is the base currency and USD is the quote currency. The rate means 1 EUR equals 1.10 USD. To convert EUR to USD, multiply by the rate. To convert USD to EUR, divide by the rate.
Rate Volatility
Major currency pairs (EUR/USD, GBP/USD) typically move 0.5-1% daily. Emerging market currencies can be much more volatile. Economic announcements, geopolitical events, and market sentiment cause rate fluctuations. High volatility means conversion costs can change quickly.