How Currency Exchange Rates Work — A Complete Guide

Blog › Finance · 10 min read · Published 2026-03-05

Understand how exchange rates are determined, the difference between fixed and floating rates, and how to get the best rates when converting money.

What Are Exchange Rates?

An exchange rate is the price of one currency expressed in terms of another currency. When you see "EUR/USD = 1.08," it means 1 Euro costs 1.08 US Dollars. Exchange rates fluctuate constantly based on supply and demand in the global foreign exchange (forex) market — the world's largest financial market, with daily trading volume exceeding $7.5 trillion.

Exchange rates affect everyone: travelers converting money, businesses importing and exporting goods, investors holding foreign assets, immigrants sending remittances home, and governments managing their economies. Understanding how they work helps you make better financial decisions and avoid unnecessary costs when converting currencies.

How Exchange Rates Are Determined

Floating Exchange Rates

Most major currencies (USD, EUR, GBP, JPY, AUD, CAD) use floating exchange rates, meaning their value is determined by market forces — supply and demand. Factors that influence demand for a currency include:

Interest rates: Higher interest rates attract foreign investment, increasing demand for that currency. When the US Federal Reserve raises rates, the USD typically strengthens.
Inflation: Countries with lower inflation see their currency appreciate over time, because their purchasing power erodes more slowly relative to others.
Economic performance: Strong GDP growth, low unemployment, and healthy trade balances increase confidence in a currency.
Political stability: Uncertainty, elections, and geopolitical tensions cause capital flight, weakening the currency.
Trade balance: Countries that export more than they import have demand for their currency (foreign buyers need local currency to pay exporters).
Market speculation: Forex traders buying and selling based on expected future movements account for a significant portion of daily volume.

Fixed (Pegged) Exchange Rates

Some countries peg their currency to another (usually USD or EUR) at a fixed rate. Examples:

Hong Kong Dollar: pegged to USD at ~7.80 since 1983
Saudi Riyal: pegged to USD at 3.75
UAE Dirham: pegged to USD at 3.6725
Danish Krone: pegged to EUR within a narrow band

Fixed rates provide stability for trade and investment but require the central bank to maintain large foreign exchange reserves to defend the peg. If reserves run low, the peg can break spectacularly (as happened to the British Pound in 1992 and the Thai Baht in 1997).

The Bid-Ask Spread

Exchange rates always come in pairs: the bid (what the dealer will pay to buy your currency) and the ask (what they'll charge to sell you a currency). The difference is the spread — the dealer's profit margin.

Interbank rate: The wholesale rate banks use with each other. Tightest spreads (0.01–0.05%). This is the "mid-market rate" you see on Google or XE.com.
Retail bank rate: What your bank charges. Typical spread: 1–3% above mid-market.
Airport exchange: Worst rates. Spread: 5–15%+. Avoid if possible.
Online services (Wise, Revolut): Typically 0.3–1% spread. Best retail option for most people.

Cross Rates and Currency Pairs

Most currencies are quoted against the USD (the world's reserve currency). To convert between two non-USD currencies, you often go through the USD as an intermediary — this is called a cross rate.

Example: Convert GBP to JPY. If GBP/USD = 1.27 and USD/JPY = 149.5, then GBP/JPY = 1.27 × 149.5 = 189.87. One British Pound buys approximately 190 Japanese Yen.

Major currency pairs (most traded): EUR/USD, USD/JPY, GBP/USD, USD/CHF, AUD/USD, USD/CAD. These have the tightest spreads and most liquidity.

Purchasing Power Parity (PPP)

PPP theory suggests that exchange rates should adjust so that identical goods cost the same across countries when expressed in a common currency. The famous "Big Mac Index" (published by The Economist) compares burger prices globally as a fun illustration:

If a Big Mac costs $5.69 in the US and 690 yen in Japan, PPP exchange rate = 690/5.69 = 121 yen/dollar
If the actual rate is 149 yen/dollar, the yen is "undervalued" by ~19% according to PPP

PPP doesn't predict short-term rates but serves as a long-term anchor. Currencies that deviate significantly from PPP tend to correct over years or decades.

How to Get the Best Exchange Rate

Avoid airport exchanges: They charge 5–15% markups. Use an ATM at your destination instead.
Use a no-foreign-transaction-fee card: Many credit cards charge 2–3% on foreign purchases. Cards like the Wise debit card or certain travel credit cards charge 0%.
Always pay in local currency: When a merchant abroad offers to charge in your home currency ("Dynamic Currency Conversion"), always decline. Their exchange rate includes a 3–5% markup. Choose the local currency and let your card issuer convert at a better rate.
Compare online services: Wise, Revolut, and OFX typically offer mid-market rates with small transparent fees, beating banks by 2–5%.
Time large conversions: Exchange rates fluctuate. For large amounts (buying property abroad, paying international tuition), monitor rates and convert when favorable. Rate alerts from services like XE or Wise can help.
Order foreign cash from your bank in advance: Better rates than exchanging at airports or tourist areas. Allow 3–5 business days for delivery.

Key Takeaways

Exchange rates are determined by interest rates, inflation, economic strength, and market sentiment. The rate you get as a consumer always includes a markup over the interbank mid-market rate — your job is to minimize that markup. Use online transfer services for large amounts, no-foreign-fee cards for travel spending, and always pay in the local currency when abroad. Understanding these fundamentals can save you hundreds or thousands of dollars on international transactions over your lifetime.