Why Do Forex Spreads Exist?

Spreads exist because someone must be willing to take the opposite side of your trade instantly. If you want to sell €10 million at 1.0850 right now, a market maker must agree to buy at that price, assuming the risk that the euro could drop 5 pips before they offload their position. That risk doesn't come free. The spread is the price of immediacy—the compensation market makers demand for holding inventory, processing orders, managing operational costs, and enduring the possibility of loss. Without spreads, no one would provide liquidity, the forex market would collapse into a slow, illiquid network of bilateral negotiations, and currency trading would become prohibitively expensive for all but the largest institutions. Understanding why spreads exist is essential because it explains why narrower spreads appear in high-volume markets (more competition, lower inventory risk) and why spreads explode during crises (higher uncertainty, greater inventory risk). This knowledge also reveals the true nature of market makers: they are not market makers because they are philanthropic. They exist because the spread gives them a profitable business model—and that model breaks down precisely when you most need liquidity.

The mechanics of the spread are rooted in three economic problems: inventory risk, adverse selection, and operational cost. Each of these forces justifies a component of the bid-ask spread, and understanding them reveals why certain spreads widen under stress and why others remain stable through market shocks.

Quick definition: Forex spreads exist because market makers must be compensated for the risk of holding inventory, the probability of trading with informed counterparties, and the cost of processing transactions and managing regulatory compliance.

Key Takeaways

• Inventory risk is the primary driver: market makers face losses if the price moves against them after they take the opposite side of your trade
• Adverse selection occurs when informed traders take advantage of market makers; spreads must widen to protect against this probability
• Operational costs—technology, compliance, clearing, settlement, regulatory capital—are baked into spreads and justify a portion of even the tightest institutional spreads
• Information asymmetry creates a cost to the market maker: you might know something they don't, so they charge a premium for the risk
• Spreads are a fundamental feature of all liquid markets, not a quirk unique to forex; the same logic applies to equities, bonds, and commodities

Inventory Risk: The Core Justification

When a market maker quotes EUR/USD at 1.0850 (bid) / 1.0852 (ask), they are taking on currency exposure. If you sell €10 million at 1.0850, the market maker now owns €10 million they did not own 1 second ago. This position has risk: if EUR/USD drops to 1.0845 in the next 2 minutes before they can lay off the position, they lose €50,000.

Inventory risk is continuous and unavoidable. A market maker cannot quote prices without assuming inventory. The spread exists to compensate them for the possibility of loss from adverse price movement. Consider a numerical example:

Scenario: USD/JPY, base case

• Quote: 145.50 (bid) / 145.52 (ask)
• Spread: 2 pips
• Your trade: You buy $10 million at 145.52
• Market maker's position: Now short ¥1,452 million

Within seconds, USD/JPY moves to 145.48. The market maker wants to offset by selling the ¥1,452 million but can only sell at 145.48, the new bid. They sell at 145.48 instead of the 145.52 they bought at. Loss: 4 pips × ¥1,452 million / 145.50 = roughly $4,000.

The 2-pip spread on the original trade generated $2,000 in revenue. The adverse move cost $4,000. Net loss on that single trade: $2,000. If this scenario occurs frequently, the market maker becomes unprofitable. To justify staying in business, they must:

1. Increase the spread to 4–5 pips to better compensate for inventory risk, or
2. Reduce inventory holding time (offset faster), or
3. Increase trading volume to amortize losses across more trades

In low-volatility environments (like EUR/USD on a quiet Tuesday), inventory risk is low, spreads compress. In high-volatility environments (like emerging-market currencies during a crisis), spreads explode because the cost of holding inventory soars.

Adverse Selection: The Hidden Tax on Market Makers

Adverse selection is a profound economic concept: the market maker faces a probability that the person on the other side of the trade knows something they don't. If a large bank's proprietary trading desk places an order to buy €50 million of EUR/USD, that bank likely has information—perhaps an upcoming economic data release they expect to favor the euro, or knowledge of a major capital flow. The market maker is at a disadvantage because the informed trader is placing the order based on private information.

The spread must widen to compensate for this asymmetry. Suppose a market maker quotes EUR/USD at 1.0850 (bid) / 1.0852 (ask). An informed trader buys €50 million at 1.0852. Thirty seconds later, positive economic data is released, and EUR/USD jumps to 1.0865. The market maker is now short €50 million at an average entry of 1.0852, facing a loss of €650,000.

This scenario is exactly why market makers fear informed order flow. They don't know which orders come from informed traders and which come from uninformed traders (e.g., a company that simply needs to exchange currencies for operations). To protect themselves, spreads must widen enough so that even when they lose to informed traders, the spread revenue on uninformed traders covers the losses.

Empirically, this effect is substantial. Research from the Bank for International Settlements (BIS) and academic studies of electronic limit-order books show that spreads widen 10–30% on the arrival of large orders because market makers perceive elevated information risk. This is why a buy order for €1 million barely moves the EUR/USD spread, but a buy order for €500 million can widen spreads 5–10 pips—market makers are protecting against the possibility that the large order is informed.

Operational Costs and Infrastructure

Beyond inventory risk and adverse selection, spreads must cover real operational costs:

• Technology infrastructure: Maintaining low-latency trading systems, matching engines, and price feeds costs hundreds of millions of dollars annually for major brokers.
• Regulatory capital: Market makers must hold capital reserves mandated by regulators. This capital could be invested elsewhere; spreads must compensate for that opportunity cost.
• Clearing and settlement: Every trade must be cleared and settled, a process that involves multiple intermediaries. Each takes a small fee.
• Compliance and legal: Forex markets are heavily regulated. Large brokers employ hundreds of compliance officers, lawyers, and auditors.
• Personnel: Traders, systems engineers, sales staff, and operations staff must be paid.

A major global bank might spend $500 million annually on forex operations—systems, personnel, compliance. That cost is spread across trillions of dollars in daily volume. Per trade, the cost is tiny—perhaps $0.05 per standard lot. But these costs are real, and they justify a portion of even the tightest spreads. During periods when trading volume falls (e.g., an economic crisis that freezes trading), fixed operational costs are spread across lower volume, forcing spreads to widen.

The Relationship Between Liquidity and Spreads

Liquidity and spreads are inversely related: more liquidity means tighter spreads; lower liquidity means wider spreads. This relationship exists because of inventory risk and the ability to quickly lay off positions.

Consider a major pair like EUR/USD. Every second, hundreds of millions of euros trade. A market maker that buys €10 million can sell it within 100 milliseconds. The inventory holding time is negligible, so inventory risk is minimal. With minimal risk, spreads can be tight—0.5–2 pips.

Now consider an exotic pair like USD/THB. Trading volume is 100 times lower. A market maker that buys $10 million might wait 30 seconds before finding a buyer. During those 30 seconds, USD/JPY could move, Thai-related news could break, or broader market conditions could shift. Inventory risk is 300× higher (30 seconds of potential adverse movement vs. 0.1 seconds). Spreads must widen accordingly—to 10–20 pips or more.

The mechanism is straightforward: if you eliminate the ability to quickly offload inventory, you increase inventory risk, and increased inventory risk increases spreads. This explains why spreads on emerging-market currencies are 5–20× wider than spreads on EUR/USD—the liquidity difference justifies the spread difference.

Information Asymmetry and the Bid-Ask Spread

A key insight from microeconomic theory is that spreads reflect the cost of information asymmetry. If you, the trader, might know something the market maker doesn't, the market maker must charge a spread to protect themselves against trading with informed parties.

This dynamic plays out especially sharply before news releases. Before the US employment report, the bid-ask spread on USD pairs widens dramatically—from 1–2 pips to 5–10 pips. Why? Because market makers know that informed traders (hedge funds, algorithms) may place orders based on information they've obtained (perhaps from talking to economists or analyzing early data flows). The spread widens to compensate for the elevated probability of trading with an informed counterparty.

Similarly, major banks widen spreads on exotic currencies when major events affecting those countries are brewing. Before a central bank decision in Brazil, spreads on USD/BRL widen from 2–3 pips to 10–15 pips because Brazilian-focused traders and hedge funds may have advance intelligence.

A Flowchart of Spread Justification

Real-World Example: The Swiss Franc Shock, January 2015

On January 15, 2015, the Swiss National Bank (SNB) unexpectedly removed its currency peg to the euro. USD/CHF had been capped at 1.20 for years. When the cap was removed, the franc surged 30% in seconds. This event illustrates all three reasons spreads exist.

Inventory risk exploded. A market maker holding Swiss franc inventory faced losses of 10–15% before they could offload. Spreads widened from 1–2 pips to 50+ pips on some pairs. Some brokers simply stopped quoting.

Adverse selection exploded. Market makers faced the terrifying possibility that they were being hit by perfectly informed traders who knew the peg would break. Every order became hostile. Spreads had to widen massively to compensate.

Operational costs mattered. With trading halted on many pairs for minutes at a time, market makers' fixed costs were not being amortized. When spreads compressed again, it took hours because the risk hadn't decreased immediately.

The franc shock cost retail forex traders hundreds of millions of dollars because spreads expanded faster than anyone's stop losses could execute. Traders expecting 5-pip spreads were filled at 50–100 pips worse than bid prices. The spread width directly reflected the three economic forces at work: inventory risk skyrocketed, adverse selection probability became nearly 100%, and operational costs were stranded against lower trading volume.

Spreads Across Market Conditions

The height of the spread at any moment reflects current market conditions. Understanding this allows you to predict when spreads will tighten or widen:

Spreads tighten when:

• Trading volume increases (more competition, faster inventory turnover)
• Volatility decreases (lower risk of adverse price movement)
• Information becomes public and symmetric (everyone has the same data)
• Time of day is peak (Asia-Europe-US overlap, maximum participation)

Spreads widen when:

• Trading volume decreases (slower inventory turnover, more risk)
• Volatility increases (higher risk of adverse movement)
• Information asymmetry emerges (rumors, pre-news uncertainty)
• Time of day is off-hours (fewer market makers participating)
• Regulatory capital becomes scarce (forces market makers to reduce positions)

Common Mistakes

1. Assuming the same spreads apply to all order sizes: A market maker might quote 2 pips on EUR/USD for orders up to €5 million, but 5 pips for orders of €100 million because of inventory risk. Larger orders face wider spreads because they create larger inventory positions.

2. Ignoring information asymmetry when trading around events: Many traders increase position sizes before major data releases, not recognizing that market makers expect informed order flow and have widened spreads 5–10×. You are trading against market makers who have priced in elevated selection risk.

3. Believing "fixed spreads" are truly fixed: Fixed spreads widen during spikes. A broker advertising "0.1-pip fixed spreads" may provide them 99% of the time but widen to 5 pips for 10 seconds during breaking news. This is when you most need liquidity but least want to pay the true cost.

4. Trading exotics expecting major-pair spreads: Exotic pairs have structurally wider spreads because of lower liquidity and higher inventory risk. Expecting USD/THB to have 2-pip spreads is misunderstanding the economics.

5. Underestimating the cost of off-hours trading: Off-hours, fewer market makers are competing, inventory risk is higher, and spreads explode 3–5×. A 2-pip spread becomes 6–10 pips. Scalpers who trade after New York closes are paying double or triple the cost for the same profit target.

FAQ

Who profits from spreads?

Market makers and brokers profit from spreads. A broker might quote you EUR/USD at 1.0850 (bid) / 1.0854 (ask)—a 4-pip spread. The broker keeps 1–2 pips and passes the remaining 2–3 pips to the interbank market to offset your position. Over millions of trades, that 1–2 pips per trade generates enormous revenue.

Can spreads ever be zero?

No. Even in the most liquid markets, zero spread is impossible because no one would provide liquidity for zero compensation. The tightest spreads in the world (major pairs between major banks during peak hours) are 0.2–0.5 pips. Below that, market makers lose money to adverse selection and operational costs.

Why do spreads widen more for selling than buying?

They usually don't—spreads are symmetric. However, if you see asymmetric spreads, it indicates market makers expect more selling pressure. If the bid-ask spread widens and the mid-price moves down, market makers are expecting more sell orders, so they widen the bid more than the ask to discourage sellers.

How do high-frequency traders affect spreads?

High-frequency traders (HFTs) are sophisticated market makers that add liquidity during quiet times. When HFTs are actively quoting, spreads compress because of increased competition. When HFTs pull back (during high-volatility periods when their losses mount quickly), spreads widen. HFTs have narrowed average spreads significantly over the past 15 years.

Are forex spreads the same across all brokers?

No. Spreads vary by broker, which reflects their access to liquidity, their market-making model, and their cost structure. A large bank with direct interbank access may quote 1-pip spreads, while a retail broker might quote 3–5 pips. Always compare spreads across brokers—the difference is substantial.

How do central bank announcements affect spreads?

Central bank announcements create asymmetry. Before a major central bank decision, insiders (sometimes) know the decision before the public. Spreads widen to compensate for this information asymmetry. After the announcement, when information is public and symmetric again, spreads compress rapidly.

Do institutional traders care about spreads?

Yes, very much. Even institutional traders trading in sizes of hundreds of millions focus intensely on spreads. A 0.5-pip spread difference on a $1 billion trade is worth $5 million. Institutions negotiate tighter spreads by trading larger volumes and maintaining credit lines with multiple market makers.

Related Concepts

• The Bid-Ask Spread
• Fixed vs Variable Spreads
• The Spread as a Trading Cost
• How Liquidity Affects Spreads
• Spreads During News Events

Summary

Forex spreads exist because market makers must be compensated for three unavoidable costs: inventory risk (the possibility that prices move against them while holding your currency), adverse selection (the possibility that they trade with informed counterparties), and operational expenses (technology, compliance, personnel). Without spreads, no one would provide liquidity, and the forex market would collapse into slow, bilateral negotiations. The spread width reflects current market conditions—tight when trading volume is high and volatility is low, wide when volume is low or volatility is high. Understanding why spreads exist reveals that they are not market friction to be eliminated but a fundamental feature of liquid markets. The traders who succeed are those who account for spreads in their strategy design and trade during times when market makers' risks (and thus spreads) are lowest.

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