Building a Trading System – Rules, Backtesting and a Trading Journal

A trading system is a written set of rules that tells you exactly when to enter a trade, when to exit with a profit, when to exit with a loss, and how much capital to risk — decided in advance, before emotion enters the picture. Without one, every decision gets made in the heat of the moment, which is precisely when human judgment is at its worst.

Start with entry rules. This should be a specific, repeatable condition: a stock breaking above a resistance level on above-average volume, a moving average crossover, or a pullback to a rising trend line. Vague criteria like "it looks strong" cannot be tested or repeated consistently. Write the exact condition down.

Next, define your exit rules — both directions. Your stop loss decides the maximum you're willing to lose on the trade, typically set below a recent support level or a fixed percentage of the entry price. Your profit target or trailing stop decides how you lock in gains. Deciding both before you enter the trade removes the temptation to move your stop further away as a loss grows, or to sell a winner too early out of fear.

Position sizing is the piece most beginners skip, and it's arguably the most important. Risking a fixed, small percentage of your total capital on any single trade — commonly 1-2% — means no single loss can seriously damage your account, even during a losing streak. A trader risking 10% per trade can be wiped out by four or five bad trades in a row; a trader risking 1% can survive dozens.

• Entry rule: the specific, repeatable condition that triggers a buy
• Stop loss: the price at which you exit if wrong, decided before entry
• Profit target: the price or condition at which you take gains
• Position size: the percentage of capital risked, kept small and consistent

Backtesting means checking how your rules would have performed on historical price data before risking real money. It won't guarantee future results, but it reveals whether a strategy has a realistic edge or is just a story that sounds good. Equally important is a trading journal — recording every trade, why you took it, and the outcome. Reviewing that journal monthly is how a system actually improves over time, because you begin to see honest patterns in what's working and what isn't, rather than relying on memory or feel.

A system doesn't remove risk. It replaces a hundred small, emotional decisions with one big, calm decision made in advance.