A day trading strategy can look pretty profitable—right before you pay for it. This sounds obvious, but it's actually one of the easiest things to forget when you are staring at a backtest showing a nice upward curve. The market does not care about that curve.
Once you trade with real money, the spread takes a slice. Commissions may take another, and slippage takes whatever is left lying around, particularly when the market moves quickly. Trade often enough and those small amounts stop looking small.
That, at least partially, is why day trading is so difficult to sustain. A study of Brazilian equity-futures traders found that 97% of individuals who continued day trading for more than 300 days lost money. The study looked at one specific market and group of traders, so, yes, it should not be treated as a universal statistic. Still, it's a useful warning: having a trading system is not the same thing as having a profitable trading business.
If you want a strategy that's profitable beyond a backtest, the first thing you need to do is calculate what each trade costs. Actually costs.
The Trade Is Never Just the Trade
As an example, let's say you buy an asset at $100 and sell it at $100.20. On the chart, you made 20 cents.
Your real result, however, depends on the price you got when you entered, the price you got when you exited, the spread at both points, any commission, and whether the order filled where you expected. If you use leverage, financing and other account-specific charges can enter the calculation, too.
The big four costs are straightforward:
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Spread: The gap between the bid and ask. You pay it when you cross from one side of the market to the other.
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Commission: The broker's explicit charge for executing the trade. A low commission is not automatically cheap if the spread is wide.
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Slippage: The difference between the price you expected and the price at which your order actually filled. It can work in your favor occasionally, but a serious trading plan should not depend on that.
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Financing: Relevant when you hold leveraged positions beyond the relevant daily cutoff. For a strategy designed to close everything within the session, it may be irrelevant, but for a strategy that regularly carries positions overnight, it is part of the math.
Then, there are less obvious costs: market-data subscriptions, platform fees, and conversion charges. Also, the opportunity cost of sitting through a long session waiting for a setup that never appears.
The SEC has previously warned that frequent trading can make commissions a significant drag on returns. The exact fee environment has changed since those older regulatory studies, particularly with the rise of zero-commission retail trading, but the basic arithmetic hasn't. More trades mean more opportunities to pay for trading.
Scalpers Face a Different Challenge
Let's take an example of two traders. Trader A takes five trades in a day and tries to capture larger intraday moves. Trader B takes 50 trades and aims to make a few points on each one. Trader B doesn't simply need a good strategy; they need inexpensive execution.
A CFD scalping strategy, for example, can target very small price movements and hold positions for minutes or even less. But when the expected gain on an individual trade is small, a spread of a few points and repeated slippage can consume a meaningful part of the gross return.
That's why copying a scalping strategy from a backtest without checking its assumed spread is asking for trouble. A strategy that makes $8 per trade with $1 of costs has a very different business model from one that makes $8 with $4.50 of costs. It's the same entries and exits, but very different outcomes.
High Win Rates Can Mask Execution Drag
Imagine a system with a 60% win rate. Sounds good. But suppose the average winning trade earns $10, the average losing trade loses $8, and your total spread, commission, and slippage averages $2 per trade.
The cost comes out of every trade, not just the winners.
Before costs, the rough expectancy is:
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(0.60 × $10) − (0.40 × $8) = $2.80 per trade
After $2 in average trading costs, only $0.80 remains. So a strategy that looked pretty healthy is operating on a very thin margin.
But real execution will not necessarily produce the same $2 average cost every day. Market conditions and liquidity change, order types matter, and breaking news can blow standard spreads wide open.
"Zero Commission" Does Not Mean Zero Cost
This deserves its own warning because the phrase is so attractive. Perhaps too attractive to novice traders.
However, a broker can charge no commission and still make money through the spread. Conversely, another broker might charge a fixed commission while offering tighter spreads. Neither pricing model is inherently superior.
What matters is the round-trip cost for the way you actually trade.
So the most practical comparison is not “Which broker has the lowest advertised fee?” That doesn't tell you a lot. Instead, ask yourself: "How much does it cost me to open and close one position under the conditions in which I actually trade?"
The Real Test Is Net Expectancy
A day trading strategy doesn't need to win most of the time. But it does need enough edge to survive its own expenses.
That is the part worth testing before you worry about finding the perfect indicator or tweaking an entry by two ticks. Calculate the spread, track the fills, add commissions. Look at slippage when the market gets ugly. Then, run the numbers again after 50 or 100 trades.
If the strategy still works after that, you have something worth studying further. If it doesn't, finding out now is considerably cheaper than finding out with a larger position.
