How to Set a Stop-Loss Order

What is a Stop-Loss?

A stop-loss is a pre-determined price at which you agree to sell a security to limit potential losses if its price falls below a certain level. The key is 'pre-determined.' If you hesitate after the price has already dropped, the psychological tendency to avoid losses can delay your selling decision. Therefore, the principle is to set a specific exit point before entering a trade.

A stop-loss is a mechanism to control the maximum amount you can lose in a single trade. If you buy a stock at $100 and set the stop-loss at $90, the risk you take in that trade is limited to $10 per share. By setting such a floor for losses, you can prevent a single mistake from jeopardizing your entire account.

This article is an educational resource explaining the principles of stop-loss orders and does not recommend buying or selling any specific securities. Appropriate criteria vary by market and security, so you should understand the principles and apply them to your own situation.

Fixed Percentage Method and Its Limitations

The simplest method is to set the stop-loss at a fixed percentage below the purchase price. If you set an 8% drop from the purchase price as your stop-loss, a stock bought at $100 would be sold at $92. This method has the advantage of clear rules, making it easy for beginners to follow, and it helps maintain a consistent loss range.

However, the fixed percentage method has the weakness of ignoring a stock's volatility. If you apply the same 8% rule to a blue-chip stock that typically moves only 1-2% a day and a growth stock that fluctuates by more than 5%, the highly volatile stock might trigger a stop-loss even during normal price swings, leading to frequent and unnecessary exits. This is why a method that adjusts the stop-loss range according to volatility is needed.

ATR-Based Stop-Loss: Adjusting for Volatility

ATR (Average True Range) is a volatility indicator that shows how much a stock moves on average per day over a certain period. Typically, a 14-day ATR is used. If the ATR is $3, it means the stock has moved by an average of about $3 per day recently. Setting the stop-loss as a multiple of ATR allows you to reflect the stock's inherent volatility.

For example, if you apply the '2 times ATR' rule to a stock with a purchase price of $100 and a 14-day ATR of $3, the stop-loss price would be $100 - (3 × 2) = $94. For stable stocks with a small ATR, the stop-loss is set closer to the purchase price, while for volatile stocks with a large ATR, it is set further away, reducing unnecessary exits due to everyday fluctuations.

ATR multiples of 2 to 3 times are commonly used, but there is no single correct answer. Increasing the multiple reduces false stop-outs but widens the potential loss, while decreasing it can lead to being stopped out even during normal price fluctuations.

Trend-Following Stop-Loss: From Highs and Moving Averages

To ride a profitable stock for as long as possible, it's useful to adjust the stop-loss upwards along with the stock price instead of keeping it fixed. A prime example is a trailing stop, where you sell if the price drops by a certain percentage from the highest point reached after entry. With a '15% from the high' rule, if a stock rises from $100 to $150, it would be sold at $127.5 (15% down from the high of $150), linking the stop-loss to the high and protecting profits.

Moving averages can also be used as a stop-loss criterion. For instance, you might sell if the closing price clearly breaks below the 20-day moving average. This aligns well with trend-following strategies, as you hold the position as long as the trend is intact and exit when there's a signal that it's breaking.

However, both methods are weak in sideways markets. In periods of aimless fluctuation, frequent exits can occur, potentially increasing costs, so these methods should be used according to the market phase.

Control Risk with Position Size, Not Just Stop-Loss Range

Setting a stop-loss alone doesn't complete risk management. The true controllable variable is 'what percentage of your account you are willing to lose in a single trade.' A common guideline is 1-2% of the account per trade. The number of shares to buy is determined by 'risk limit ÷ stop-loss range.' If you have an account of $10,000 and limit your risk to 1% ($100), and the difference between the purchase price and the stop-loss is $10 per share, then the number of shares to buy would be $100 ÷ $10 = 10 shares.

This formula leads to the conclusion that for stocks with a wider stop-loss range, you should buy fewer shares. This is because if the distance to the stop-loss is greater, you must reduce the quantity to maintain the same risk limit.

By fixing risk at a constant percentage, your account will decrease slowly even with consecutive losses. If you lose 1% per trade, even five consecutive stop-outs would result in a loss of only about 5%, remaining within a recoverable range.

Common Pitfalls and Checkpoints

The most common mistake is setting a stop-loss but then, when it's hit, moving the threshold down, thinking 'let's wait a little longer.' The moment you move the stop-loss lower, the rule is nullified, and you enter the typical path where a small loss grows into a large one. A stop-loss is just a number on paper if it's not executed.

Another pitfall is placing the stop-loss at an obvious spot, such as just below a widely recognized support level. If stop-loss orders accumulate around that area, the price can easily get caught in temporary fluctuations, hitting that level before rebounding. Giving a little extra room below the support level or considering an ATR-based distance can help reduce such noise.

In summary, check three things. First, did you set a numerical stop-loss before entering the trade? Second, is that distance reasonable given the stock's volatility (e.g., ATR, percentage from the high)? Third, did you adjust your position size to match that stop-loss range? When these three factors align, a stop-loss becomes a rule that protects your account, rather than a fear that amplifies losses.