How Forex Spreads Actually Work (and Why They're Not Free)

What a spread actually is

The spread is the difference between the bid price (what you can sell at) and the ask price (what you can buy at) for any instrument, at any given moment. It's not a fee charged separately, it's built directly into the two prices you're quoted. Buy at the ask, and the instrument has to move in your favor by at least the spread amount before the trade is even at breakeven.

This makes the spread the most immediate cost in trading, and the one most beginners underestimate, since it doesn't show up as a separate line item the way a commission does. It's simply the gap you have to cross before a trade becomes profitable at all.

Why spreads aren't fixed, even on the same instrument

Spreads widen and narrow based on liquidity and volatility, not just which broker or account type is being used. During the overlap between the London and New York trading sessions, when the most participants are active in major pairs, spreads on something like EUR/USD can compress to nearly nothing on a tight ECN account. During the quieter Asian session, or around major news releases when liquidity providers pull back to avoid getting caught on the wrong side of a fast move, that same spread can widen to several times its normal size.

This is why a strategy that looks fine on a backtest using average spread assumptions can perform noticeably worse in live conditions if it happens to trade frequently during periods when spreads are naturally wider, particularly around scheduled news events.

How the spread compounds for active traders

A cost that looks trivial on a single trade becomes significant at volume. A trader taking ten round-trip trades a day, each crossing a small spread, is paying that cost ten times daily, every trading day. Over a month, a seemingly small per-trade cost adds up to a real, recurring drag on returns, one that exists regardless of whether the underlying strategy is profitable or not.

This is exactly why overtrading is more expensive than it first appears. Extra trades taken outside a strategy's actual criteria don't just carry their own win/loss risk, they also each cross a spread, adding a cost that erodes the edge of the legitimate trades even when the extra trades themselves happen to break even.

Fixed versus variable spread models

Some brokers, typically market maker models, offer fixed spreads that don't change regardless of market conditions, trading predictability for a generally wider baseline cost. Others, typically ECN models, offer variable spreads that track real market liquidity closely, tighter most of the time, but capable of widening significantly during volatile or illiquid periods.

Neither model eliminates the cost, they distribute it differently. A fixed-spread account pays a steady cost regardless of conditions. A variable-spread account often pays less during normal conditions and more during volatile ones, precisely when a wider spread is most likely to matter for a trade already under pressure from fast price movement.

Spread as a real input into whether a trade is worth taking

The spread should factor directly into position sizing and target-setting, not just get treated as background noise. A very short-term strategy with a small profit target that's only a few times larger than the typical spread on that instrument is operating with much less real margin than the raw price target suggests. Checking the typical spread on an instrument, especially during the specific session a strategy tends to trade in, is a basic but frequently skipped step in evaluating whether a strategy's numbers hold up once real trading costs are included.