Currency Exchange Explained: How Exchange Rates Work and Why They Change

Currency exchange is the conversion of one currency into another at an exchange rate. The exchange rate tells you how much of the second currency one unit of the first currency can buy. The amount a customer actually receives may differ from a market or reference rate because providers can apply bid-ask spreads, exchange-rate margins and separate transaction fees.

That difference between the market rate and the customer rate is one of the most important things to understand about currency exchange.

A traveler may see one exchange rate online, another at an airport exchange counter and a third inside a banking app.

None of those numbers necessarily means that one source is wrong.

They can represent different things:

• a reference rate;
• an interbank market rate;
• a dealer’s buying rate;
• a dealer’s selling rate;
• a card-network conversion rate;
• a rate containing a provider margin.

Understanding which rate you are looking at is more useful than simply searching for the biggest number.

What Is Currency Exchange?

Currency exchange is the process of converting monetary value denominated in one currency into monetary value denominated in another.

For example, a person may exchange:

• U.S. dollars for euros;
• euros for British pounds;
• Malaysian ringgit for U.S. dollars;
• Japanese yen for Singapore dollars.

The exchange rate establishes the conversion relationship.

If EUR/USD is quoted at 1.15, one euro can be exchanged at the quoted market relationship for approximately 1.15 U.S. dollars.

The European Central Bank defines an exchange rate as the rate at which one currency can be exchanged for another.

However, the rate visible to a consumer may not be the same rate at which large financial institutions trade currencies.

That distinction becomes important whenever money is actually converted.

How an Exchange Rate Works

Every foreign exchange transaction involves two currencies.

One currency is being sold while another currency is being bought.

A currency pair therefore has two sides.

Consider:

EUR/USD = 1.1500

This means that one euro is worth 1.15 U.S. dollars under that quotation.

EUR is the base currency.

USD is the quote currency.

The rate answers the question:

How many units of the quote currency are required for one unit of the base currency?

If the rate rises from 1.1500 to 1.1800, one euro buys more dollars than before.

In that quotation, the euro has strengthened relative to the dollar.

If the rate falls to 1.1000, one euro buys fewer dollars.

The euro has weakened relative to the dollar.

Currency Exchange Example

Suppose a traveler wants to convert €1,000 into U.S. dollars.

If the applicable exchange rate is:

EUR/USD = 1.15

the simple mathematical conversion is:

€1,000 × 1.15 = $1,150

But the traveler may not actually receive $1,150.

A currency provider could offer a customer rate of 1.12.

The conversion would then be:

€1,000 × 1.12 = $1,120

The difference is $30 before considering any separate service fee.

This demonstrates why the phrase “zero commission” does not necessarily mean free currency exchange.

The provider can earn money through the exchange rate itself.

Market Rate vs Customer Exchange Rate

A major source of confusion is the assumption that there is one universal exchange rate at every moment.

There is not.

Different rates serve different purposes.

A reference rate should therefore not automatically be interpreted as a rate that a consumer is entitled to receive.

The ECB makes this distinction unusually explicit.

Its June 2026 framework states that euro foreign exchange reference rates are intended for information purposes rather than for use directly or indirectly in market transactions. The ECB normally determines those rates around 14:10 CET.

That is an important practical lesson:

A reference exchange rate describes a market relationship; it is not a retail price guarantee.

What Is the Bid-Ask Spread?

Currency dealers generally quote two prices.

The bid is the price at which the dealer is willing to buy a currency.

The ask is the price at which the dealer is willing to sell it.

The difference is the bid-ask spread.

For example:

The spread is:

1.1580 − 1.1420 = 0.0160

The spread helps compensate the provider for costs and risks associated with supplying currency liquidity.

Retail customers often encounter a wider effective spread than major institutions because smaller transactions can have different operating costs, competition and pricing structures.

Information Gain: The Exchange Rate Margin Can Be a Hidden Fee

Consumers often compare foreign exchange providers by looking only at the visible transaction fee.

That can produce the wrong comparison.

The World Bank’s Remittance Prices Worldwide methodology treats the exchange-rate margin as an important component of transaction cost because the provider may apply a rate different from the market reference rate. The margin may not appear as a separately quoted transfer fee.

This creates a useful rule:

Compare the final amount received, not just the advertised fee.

A provider advertising a $0 transfer fee can still be more expensive than a provider charging $5 if the first provider uses a substantially worse exchange rate.

For currency exchange, the headline fee is therefore only part of the price.

How to Calculate the Real Cost of Currency Exchange

The simplest retail comparison uses four numbers:

1. Amount being exchanged
2. Neutral reference rate
3. Rate actually offered
4. Any separate fees

Imagine a reference rate of:

1 USD = 4.50 MYR

You want to exchange $1,000.

At the reference rate:

$1,000 × 4.50 = MYR 4,500

Provider A offers:

4.43 MYR per USD

and charges no separate fee.

You receive:

$1,000 × 4.43 = MYR 4,430

The exchange-rate difference costs the equivalent of MYR 70.

Provider B offers:

4.48 MYR per USD

but charges a MYR 20 fee.

The gross conversion is:

MYR 4,480

After the fee:

MYR 4,460

Provider B has the visible fee but produces the better final result.

That is why final delivered value is usually a better comparison metric than commission alone.

The Foreign Exchange Market Is Much Larger Than Retail Currency Exchange

Airport exchange counters and banking apps represent only a tiny visible part of the global foreign exchange system.

The Bank for International Settlements reported that average turnover in over-the-counter foreign exchange markets reached $9.6 trillion per day in April 2025, up 28% from $7.5 trillion per day in the 2022 survey.

Spot foreign exchange transactions alone averaged approximately $3 trillion per day and represented 31% of total global FX turnover.

FX swaps were even larger, averaging about $4 trillion per day and representing 42% of turnover.

This matters because the exchange rate seen by an individual customer ultimately sits on top of a much larger wholesale market involving:

• banks;
• institutional investors;
• corporations;
• hedge funds;
• central banks;
• dealers;
• trading platforms.

Retail currency conversion is therefore one endpoint of a global pricing and liquidity network.

Why the U.S. Dollar Matters So Much

Currency trading is organized in pairs, but some currencies appear far more frequently than others.

The U.S. dollar remains dominant.

According to the BIS 2025 Triennial Survey, the U.S. dollar was on one side of 89.2% of all foreign exchange trades measured in April 2025.

The euro appeared on one side of 28.9% of trades, while the Japanese yen accounted for 16.8%.

The percentages add to more than 100% because every FX transaction contains two currencies.

Dollar dominance also helps explain why some less frequently traded currency pairs are effectively priced through a major currency.

For example, two currencies with limited direct trading may each trade actively against the U.S. dollar, allowing a cross rate to be calculated.

What Is a Cross Exchange Rate?

A cross rate is an exchange rate derived from two related currency quotations.

Suppose:

USD/MYR = 4.50

and:

USD/SGD = 1.35

To estimate the MYR/SGD relationship:

4.50 ÷ 1.35 ≈ 3.33

This implies approximately:

1 SGD = 3.33 MYR

Real markets include bid-ask spreads, execution differences and continuously changing prices, so actual tradable rates can differ.

But the example explains an important structural concept:

Not every currency pair needs an equally deep direct market if both currencies trade actively against another liquid currency.

The ECB’s own 2026 reference-rate framework recognizes this structure. When direct euro trading is insufficient for certain currencies, its methodology can use rates against another major liquid currency to calculate the euro cross rate.

Why Exchange Rates Change

Floating exchange rates respond continuously to supply and demand for currencies.

That demand can change for many reasons.

Interest Rates

Higher interest rates can make assets denominated in a currency more attractive, particularly when investors expect the higher return to persist.

However, the relationship is not mechanical.

Markets also price expectations.

A central bank can raise rates while its currency falls if investors expected an even larger increase or believe economic conditions are deteriorating.

Inflation

Persistently higher inflation reduces the purchasing power of money.

Over longer periods, substantial differences in inflation can influence exchange-rate relationships.

Again, the adjustment may be uneven because capital flows, policy expectations and economic conditions can dominate in the short term.

Economic Growth

Strong growth can increase investment demand for a country’s assets and currency.

Weak growth can reduce that demand.

But rapid growth can also create inflation or trade imbalances, so growth alone does not determine a currency’s direction.

Central Bank Policy

Interest-rate decisions, asset purchases, liquidity programs and policy communication can change expectations about future currency conditions.

Markets often react before a policy decision is formally announced because traders price probabilities.

Trade

Countries receive foreign currency when exporting goods and services and need foreign currencies when importing.

Changes in trade flows can therefore influence supply and demand in FX markets.

Capital Flows

Foreign investment can create demand for a currency.

Capital leaving a country can create selling pressure.

Portfolio investment can move rapidly, making financial flows especially important over shorter periods.

Political and Financial Risk

Elections, geopolitical shocks, banking stress, debt concerns and unexpected policy changes can alter investor risk appetite.

Currencies perceived as exposed to a particular shock may weaken quickly.

Commodity Prices

Currencies of economies that rely heavily on commodity exports can be influenced by prices for oil, metals, agricultural products or other major exports.

Exchange Rates Move Because Expectations Move

One of the most important principles in foreign exchange is that markets respond to new information relative to expectations.

Imagine economists expect a central bank to raise its policy rate by 0.25 percentage points.

The central bank does exactly that.

The currency may barely move because the decision was already expected.

If the bank unexpectedly raises the rate by 0.50 percentage points, the market reaction can be much larger.

The event itself is not enough to explain the movement.

The relevant question is:

How did the new information differ from what market participants had already priced?

This is why explanations such as “the currency rose because rates increased” are often incomplete.

Floating vs Fixed Exchange Rates

Not every currency is allowed to move freely.

Exchange-rate arrangements exist along a spectrum.

Floating Exchange Rate

A floating rate is largely determined through market supply and demand.

Central banks can still influence conditions through monetary policy or direct intervention.

Managed Float

The market determines much of the rate, but authorities may intervene to reduce volatility or influence the currency’s path.

Pegged Exchange Rate

A currency can be linked to another currency or basket at a chosen relationship.

Authorities then use policy tools and reserves to maintain the arrangement.

Currency Board or Similar Hard Peg

Some systems impose stronger institutional requirements designed to maintain a tightly defined exchange relationship.

The practical point for consumers is simple:

The forces determining an exchange rate depend partly on the currency regime.

A freely floating currency and a tightly managed currency should not be analyzed using exactly the same assumptions.

Why Currency Rates Differ Between Providers

Suppose five websites display five slightly different USD/EUR rates at the same moment.

Several explanations are possible.

Different Data Times

Currency prices can move from second to second.

A rate captured one minute earlier may already differ.

Different Data Sources

Providers may receive quotes from different banks, trading venues or market-data suppliers.

Bid, Ask or Mid-Market Rate

One service may display the midpoint between bid and ask prices.

Another may show an executable buy or sell price.

Provider Margin

A bank, money changer or payment company may add its own margin.

Customer Type

Large institutional clients can receive different pricing from individuals making small conversions.

Transaction Size

A very large transaction may receive individually negotiated pricing.

Currency Liquidity

Major currency pairs usually have deeper markets than thinly traded currencies.

The ECB’s methodology explicitly notes that market liquidity can differ greatly between liquid major currencies and less liquid exotic currencies, as well as at different times of day.

Therefore, two different exchange-rate quotes can both be legitimate while serving different purposes.

What Does “Mid-Market Exchange Rate” Mean?

The mid-market rate is commonly calculated around the midpoint between buying and selling prices.

If:

Bid = 1.1490

and:

Ask = 1.1510

then the midpoint is approximately:

1.1500

This can be useful as a comparison reference.

But the midpoint is not necessarily an executable retail rate.

A provider must still determine the price at which it is willing to buy or sell the currency.

This is similar to other financial markets: a midpoint can describe where the market sits without guaranteeing that a customer can complete an unlimited transaction at that exact number.

How Official Reference Rates Are Produced

Official reference rates can look authoritative enough to be mistaken for universal transaction prices.

The ECB methodology shows why that interpretation is incorrect.

As of its June 2026 framework:

• the rates are normally determined around 14:10 CET;
• the process uses market information and transaction data where sufficiently liquid;
• bid and offer rates or previous transactions can be used in less liquid conditions;
• data undergo tolerance checks;
• multiple central banks participate in validation;
• published rates are intended primarily for information.

The framework even specifies that a quote more than 30 seconds old should generally not be considered actively traded unless the exchange rate shows limited volatility.

That detail demonstrates how quickly the underlying market can change.

Currency Exchange at Banks vs Money Changers vs Digital Services

The best provider cannot be identified from the business type alone.

Different channels compete on different combinations of price and convenience.

Some digital payment providers can also hold customer value electronically before a conversion or payment takes place. The underlying balance may operate differently from a bank deposit, as explained in our guide to electronic money and e-money.

A consumer should therefore compare the complete transaction, not the brand category.

The Four-Layer Cost of Currency Conversion

A useful way to audit a currency conversion is to break the cost into four layers.

Layer 1: Exchange Rate

What rate is being applied?

Layer 2: Exchange-Rate Margin

How far is that rate from a reasonable market or reference rate?

Layer 3: Explicit Fee

Is there a fixed or percentage conversion fee?

Layer 4: Additional Transaction Costs

Possible additional costs include:

• transfer fees;
• card charges;
• ATM fees;
• receiving fees;
• intermediary fees.

A low number in one layer can be offset by a high number in another.

This is why asking “What is your fee?” is less useful than asking:

“How much of the destination currency will I receive after all charges?”

Currency Exchange and International Money Transfers

Currency exchange often forms part of an international transfer.

The sender provides one currency, while the recipient receives another.

The total cost can therefore combine:

transfer fee + exchange-rate margin + possible receiving/intermediary costs

World Bank methodology specifically measures both transfer fees and foreign-exchange margins when comparing remittance prices.

The data also show why FX margins should not be ignored.

In the World Bank’s Q2 2024 dataset, fluctuations in the average cost of sending $200 through mobile operators since 2021 were largely associated with changes in the average foreign-exchange margin rather than simply the stated transfer fee.

We will cover this cost structure in greater depth in the International Transfers section.

Does Cryptocurrency Have an Exchange Rate?

Crypto assets also trade against national currencies, so a price such as BTC/USD can be described as an exchange relationship.

However, exchanging one sovereign currency for another is structurally different from buying a market-priced crypto asset.

A conventional exchange rate compares two monetary units.

A crypto price may compare national currency with an asset whose value is determined by crypto-market supply and demand and which may not represent an issuer liability.

Our guide to digital currency vs cryptocurrency explains that distinction in more detail.

Common Currency Exchange Mistakes

1. Comparing Only the Advertised Fee

A zero-fee service can contain a large exchange-rate margin.

Better approach: compare the final amount received.

2. Treating a Reference Rate as a Guaranteed Customer Rate

An official or mid-market reference may not be directly executable.

Better approach: distinguish informational benchmarks from actual transaction quotes.

3. Reading the Currency Pair Backwards

USD/EUR and EUR/USD are reciprocal quotations.

Confusing them can produce an obviously incorrect conversion.

Better approach: identify the base and quote currency first.

4. Ignoring Rate Expiration

A quoted rate may change before a transaction is confirmed.

Better approach: determine whether the provider guarantees the rate and for how long.

5. Accepting an Optional Conversion Without Checking It

ATMs and merchants can sometimes offer to convert a foreign transaction into the cardholder’s home currency.

The convenience of seeing a familiar currency does not prove that the conversion is cheaper.

Better approach: inspect both the rate and any additional fee before accepting.

6. Assuming All Currency Markets Are Equally Liquid

Rates for heavily traded currencies can behave differently from those for currencies with limited trading.

Better approach: expect pricing differences to widen when liquidity is weaker.

A Practical Seven-Step Currency Exchange Check

Before exchanging a meaningful amount of money, use this framework.

Step 1: Confirm the Currency Pair

Know exactly which currency you are selling and which you are buying.

Step 2: Check a Neutral Reference

Use a reputable central-bank or established market reference to understand the approximate current relationship.

Do not assume that reference is itself a retail offer.

Step 3: Get the Provider’s Actual Quote

Look at the rate that will apply to your transaction.

Step 4: Calculate the Converted Amount

Multiply or divide according to the quotation.

Step 5: Subtract All Explicit Fees

Include fixed and percentage charges.

Step 6: Check for Additional Costs

Consider card fees, ATM charges, transfer costs or receiving charges.

Step 7: Compare Final Amounts

For two providers, compare:

How much destination currency arrives after every cost?

That single number removes much of the marketing noise around currency exchange.

Why “Best Exchange Rate” Is an Incomplete Question

The best-looking exchange rate may not produce the best transaction.

Suppose Provider A offers:

4.50

with a 2% conversion fee.

Provider B offers:

4.46

with no fee.

Depending on the amount and fee calculation, Provider B may still deliver more money.

Timing also matters.

A slightly better rate today is irrelevant if the customer needs the funds next month and the provider does not lock the rate.

The more useful question is therefore:

Which option provides the best final value for this amount, currency pair, payment method and transaction time?

That question incorporates the conditions that actually determine cost.

How Large Is Concentration in FX Trading?

Foreign exchange is global, but trading activity is geographically concentrated.

BIS data show that sales desks in the United Kingdom, United States, Singapore and Hong Kong SAR accounted for 75% of total FX trading on the survey’s net-gross basis in April 2025.

This is useful context because a global 24-hour market does not mean trading activity is evenly distributed around the world.

Liquidity shifts as major financial centers open and close.

This can affect spreads, volatility and the depth available in particular currency pairs.

When Is an Exchange Rate “Good”?

There is no universally good exchange rate independent of context.

A useful rate comparison requires at least:

• the currency pair;
• transaction direction;
• amount;
• market reference;
• provider margin;
• fees;
• timing.

A customer exchanging $100 in cash has different pricing conditions from a corporation hedging $10 million of future foreign revenue.

Calling one rate “good” without those conditions removes the information necessary to evaluate it.

Key Takeaways

• Currency exchange converts one currency into another using an exchange rate.
• An exchange rate states the value of one currency relative to another.
• A market or reference rate is not necessarily the rate available to a retail customer.
• Currency providers can earn through a bid-ask spread or exchange-rate margin, even when the advertised commission is zero.
• The best comparison is usually the final amount received after the exchange rate and all fees.
• Global OTC foreign exchange turnover averaged $9.6 trillion per day in April 2025, according to the BIS.
• The U.S. dollar was on one side of 89.2% of global FX trades measured in the 2025 BIS survey.
• Currency rates move in response to monetary policy, inflation, economic expectations, trade, capital flows, risk and other changes in supply and demand.
• A cross rate can be calculated through another major currency when direct trading between two currencies is limited.
• Reference rates are informational benchmarks; the ECB explicitly states that its euro foreign exchange reference rates are not intended as transaction benchmarks.
• A zero-fee currency conversion is not automatically a zero-cost conversion.
• “Best exchange rate” is meaningful only when transaction amount, direction, timing and total fees are specified.

Frequently Asked Questions

What is currency exchange?

Currency exchange is the process of converting monetary value from one currency into another. The conversion uses an exchange rate that expresses the relative value of the two currencies. The actual customer rate can include a spread or provider margin in addition to separate transaction fees.

What is an exchange rate?

An exchange rate shows how much of one currency can be obtained for another. For example, an EUR/USD rate of 1.15 indicates that one euro corresponds to approximately 1.15 U.S. dollars under that quotation.

Why do exchange rates change?

Exchange rates change when supply and demand for currencies change. Important influences include interest rates, inflation, economic expectations, central-bank policy, capital flows, trade conditions, commodity prices and political or financial risk.

Why is my bank’s exchange rate different from the rate online?

An online rate may be a market midpoint or reference rate, while a bank can provide an executable customer rate containing a spread or margin. Rates can also differ because of timing, data sources, transaction size and fees.

What is the difference between a buy rate and a sell rate?

The buy rate is generally the rate at which a currency provider buys a currency from a customer. The sell rate is the rate at which the provider sells that currency. The difference contributes to the provider’s spread.

Does zero commission mean currency exchange is free?

No. A provider can charge no explicit commission while earning a margin through the exchange rate. Compare the final amount of destination currency received rather than relying only on the advertised fee.

What is a reference exchange rate?

A reference exchange rate is an informational benchmark produced under a defined methodology. For example, the ECB’s euro reference rates are normally determined around 14:10 CET and are intended primarily for information rather than as rates for market transactions.

What is a cross exchange rate?

A cross exchange rate derives the relationship between two currencies from their rates against another currency. Cross rates are useful when direct trading between the two currencies is less active.

What is the forex market?

The foreign exchange, or FX, market is the global market in which currencies are traded. BIS data show OTC FX turnover averaged $9.6 trillion per day in April 2025.

How can I compare currency exchange providers?

Compare the actual exchange rate, exchange-rate margin, explicit fees and any additional transaction costs. Calculate how much destination currency you receive after all costs. The provider delivering the highest net amount generally offers the better financial result for that specific transaction.

Final Thoughts

Currency exchange looks simple because the final calculation can be simple.

Multiply one amount by an exchange rate and receive another currency.

The pricing underneath that transaction is more complicated.

A market price can sit behind a reference rate, a dealer spread, a customer rate and several separate fees before the final amount reaches the user.

That leads to one practical principle:

Do not evaluate currency exchange by the advertised commission or headline rate in isolation. Evaluate the complete conversion from the amount you give up to the amount you actually receive.

The same principle works whether currency is exchanged at a bank, money changer, digital service or as part of an international transfer.

Once the user separates the reference rate, transaction rate, exchange-rate margin and explicit fees, currency exchange becomes much easier to compare.