I watched a trader celebrate a 2% move on a stock — right before realising he'd lost money. He'd bought at the ask, sold at the bid, and the spread ate 2.5% of his capital before the market even moved. The trade was perfect. The execution killed him.
The bid-ask spread is the difference between what buyers will pay and what sellers demand. It's market maker profit margin, transaction cost, and liquidity gauge all rolled into one number. On liquid instruments like ES futures, you might pay one tick. On a thinly traded small cap, you're handing over 3-5% just to get in. Most retail traders ignore this until they're deep in a position that's already underwater — not from price movement, but from the spread itself.
I learned this the hard way scalping ASX small caps in 2011. Every entry cost me half the move I was chasing. I was picking direction correctly 60% of the time and still bleeding capital. The math was simple once I wrote it down: ten trades a day at 1% spread cost = 10% monthly overhead before profit. My edge had to clear that bar before I saw a dollar.
The fix: trade liquid instruments during active hours. Use limit orders that sit inside the spread when possible. Calculate spread cost as a percentage of your intended profit target — if the spread is 30% of your target, you're gambling, not trading. On the ASX, stick to the top 50 stocks during 10am-3pm. On US markets, avoid the first and last 15 minutes unless you're specifically trading volatility. The bid-ask spread isn't just a number on your screen — it's a recurring cost that compounds over hundreds of trades. Treat it like any other transaction cost, factor it into your trade expectancy, and avoid instruments where the spread alone kills your edge before the first tick moves. The market charges rent for access — don't pay more than you have to.
This content is educational only and does not constitute financial advice. Past performance is not indicative of future results. Always seek licensed financial advice before trading.