What Is a Stop-Loss Order?
A stop-loss order is an instruction you give your broker to automatically sell a stock when its price falls to a level you specify. It is one of the simplest and most effective risk-management tools available to any investor. The purpose is straightforward: limit how much you can lose on a single position without requiring you to watch the market constantly.
For example, if you buy a stock at $100 and set a stop-loss at $90, your broker will automatically place a sell order if the price drops to $90. Your maximum loss is roughly $10 per share (plus fees and slippage), regardless of what happens next.
Stop-Loss vs Stop-Limit: Know the Difference
There are two main types of stop orders, and the distinction matters:
- Stop-loss (stop-market) order: When the stop price is hit, it becomes a regular market order. Your shares will sell, but the actual execution price might be lower than your stop price in fast-moving markets — this is called slippage.
- Stop-limit order: When the stop price is hit, it becomes a limit order at a specific price you choose. You get price protection, but there is no guarantee the order fills. In a crash, your stop-limit might never execute, leaving you holding the stock.
For most investors protecting against large losses, the standard stop-market order is preferable because execution certainty matters more than a few cents of price improvement.
Where to Set Your Stop-Loss
There is no universal "right" stop level, but several frameworks help you decide:
Percentage-Based Stops
The simplest approach: set your stop a fixed percentage below your purchase price. Common ranges:
- 5-7% for short-term or momentum trades where you want tight risk control.
- 10-15% for swing trades or medium-term positions.
- 15-25% for long-term investments where normal volatility should not knock you out.
The trade-off: tight stops get triggered more often by routine price swings; wide stops mean larger potential losses per trade.
Technical Stops
Place your stop just below a meaningful technical level:
- Below a support level on the chart — if support breaks, the thesis may be wrong.
- Below a moving average that the stock has respected (e.g., the 50-day MA for medium-term holds).
- Below a recent swing low — if price makes a lower low, the trend has shifted.
Technical stops are context-aware: they adapt to the stock's actual volatility rather than applying an arbitrary percentage.
Volatility-Based Stops (ATR)
The Average True Range (ATR) measures how much a stock typically moves per day. A common method is to set your stop 2-3 times the ATR below your entry (or below the current price if already in profit). This gives the stock room to breathe based on its own behavior, not a fixed number you made up.
Trailing Stops: Locking In Profits
A trailing stop moves up with the stock price but never moves down. As the stock rises, your stop rises with it. If the stock falls, the stop stays where it was, protecting your gains.
- Example: You buy at $100 with a 10% trailing stop. The stock rises to $150 — your stop is now at $135. If it falls to $135, you sell with a $35 per share gain locked in.
Trailing stops are excellent for trend-following strategies. The downside: they can get triggered by normal pullbacks within an ongoing uptrend, kicking you out of a position that would have continued higher.
Common Stop-Loss Mistakes
- Setting stops too tight: A 2-3% stop on a volatile stock will almost certainly get triggered by noise. You end up with many small losses that add up.
- Setting stops at obvious round numbers: Many traders put stops at $50, $100, etc. These levels attract predatory algorithms that push price through the level to trigger stops and then reverse. Place your stop just below the obvious level (e.g., $49.75 instead of $50).
- Moving your stop down: When price approaches your stop, the temptation to "give it more room" is strong. This defeats the purpose. If your original analysis was wrong, accept the loss.
- Not using stops at all: Hoping a losing stock "comes back" is one of the most expensive mistakes in investing. A $10,000 position that drops 50% needs a 100% gain just to break even.
- Cancelling stops before earnings: Earnings gaps can blow right past your stop. Decide in advance whether you want to hold through earnings or exit before — do not remove protection at the last minute.
Stop-Losses in Gap-Down Scenarios
A critical limitation: stop-market orders do not guarantee your stop price. If a stock closes at $60 and opens the next morning at $45 (earnings miss, bad news overnight), your stop at $55 triggers but fills near $45. Your actual loss is $15, not $5. This is called gap risk.
To manage gap risk:
- Be aware of scheduled events (earnings, FDA decisions, economic reports) that could cause gaps.
- Consider reducing position size before high-risk events rather than relying on stops alone.
- Use options (protective puts) for positions where gap risk is unacceptable.
Stop-Loss and Position Sizing
Your stop level should directly inform how many shares you buy. The formula:
Position size = Risk amount / (Entry price - Stop price)
Example: You want to risk no more than $500 on a trade. You enter at $100 with a stop at $92.
Position size = $500 / ($100 - $92) = $500 / $8 = 62 shares.
This ensures that no single trade can lose more than your predetermined risk amount. This is how professional traders manage risk — not by guessing share counts, but by calculating them from the stop distance.
When Not to Use Stop-Losses
Stop-losses are not always appropriate:
- Long-term index fund investors adding to a broad-market ETF over decades do not need stops. Time and diversification handle the risk.
- Illiquid stocks with wide bid-ask spreads may suffer terrible fills on stop triggers.
- After-hours and pre-market: Most broker stop orders only activate during regular session hours. Extended-hours moves can blow through your stop before it activates.
For most individual stock positions and active portfolios, however, stop-losses remain one of the best tools for keeping losses small and predictable.
Key Takeaways
- A stop-loss automatically sells when price hits your predetermined level — no discipline required in the heat of the moment.
- Use technical or volatility-based levels rather than arbitrary percentages.
- Trailing stops protect profits by moving up with the stock price.
- Gap risk means your actual fill may be worse than your stop price.
- Your stop distance should determine your position size, not the other way around.
- Long-term passive investors in diversified index funds generally do not need stops.