Direct answer
Forex spreads change because the bid-ask spread is not a fixed fee: it responds to changing supply and demand for liquidity, trading costs for market makers or liquidity providers, and their assessment of short-term risk. When these factors make trading more difficult or riskier, the ask and/or bid prices can move further apart, widening the spread. When conditions become calmer and more liquid, spreads typically narrow.
How the bid-ask spread works in practice
A bid-ask spread is the difference between the bid price (what buyers are willing to pay) and the ask price (what sellers are willing to accept). In many trading setups, spreads are influenced by:
- Liquidity: If many participants are ready to trade at similar prices, matching orders is easier and the spread can be smaller. If fewer orders are available, the spread can widen.
- Volatility: Rapid price movement increases the chance that a quoted price will become outdated before a trade occurs. Widening spreads help compensate for this uncertainty.
- Order flow and imbalance: When buy pressure or sell pressure is stronger than the other side, the market may not have matching liquidity at the same prices, increasing the spread.
- Trading costs and capacity: Liquidity providers may face higher operational or hedging costs during stressed market periods, affecting how tightly they can quote.
- Execution venue and quote model: Different platforms and liquidity sources can produce different effective spreads because they may connect to different order books or use different execution approaches.
Example checks you can do
Even without real-time data, you can understand spread changes by checking whether the market condition changed:
- Low-liquidity hours: During less active trading periods, spreads often widen because fewer participants quote prices.
- High-news volatility windows: When major information is released, short-term uncertainty rises, and spreads often widen.
- Comparing currency pairs: Pairs with consistently heavier trading typically show tighter spreads than less-traded pairs, all else equal.
For verification, compare the spread shown on your quote screen at different moments and note whether it coincides with reduced liquidity or heightened movement in the underlying exchange rate.
Limitations and uncertainty
Spreads can change for multiple overlapping reasons at the same time, so any single explanation is incomplete. Spread behavior is also venue-dependent: what you see may reflect the specific provider’s liquidity sources and execution model. This article does not assume real-time data, and it does not predict future changes; it only describes general mechanisms and how they relate to bid and ask pricing.