Position sizing and stop-losses

Survive the trades where you're wrong

The most important decisions in trading are often not what you buy, but how much you buy and where you'll exit if you're wrong. Position sizing and stop-losses are the foundation of risk management. They protect your capital, limit emotional decision-making and ensure that no single trade can significantly damage your account.

Successful traders understand a simple truth: you don't need to be right on every trade. You need to survive the trades where you're wrong.

Risk comes before reward

Before entering any trade, answer three questions. Only after they are answered should you decide how many shares to buy.

• Where will I enter?
• Where will I exit if I'm wrong?
• How much can I safely lose?

Stop first, size second

Many beginners start with position size and then look for a stop-loss. Experienced traders do the opposite.

The 1% risk rule

A common guideline is to risk no more than 1% of your account on a single trade. This means that if your stop-loss is hit, your total loss should not exceed 1% of your portfolio value.

Keeping losses small has a powerful mathematical advantage. Large losses require disproportionately large gains to recover:

• A 5% loss needs a 5.3% gain to recover.
• A 10% loss needs an 11.1% gain to recover.
• A 20% loss needs a 25% gain to recover.
• A 50% loss needs a 100% gain to recover.

Keep losses manageable

Small losses are easier to overcome. The goal is not to avoid losses entirely. The goal is to keep them manageable.

Calculating position size

Position size should be determined by your predetermined risk, not by how confident you feel about a trade. The formula is: position size (shares) = (account size × risk percentage) ÷ (entry price − stop price). For example:

• Portfolio value: $10,000. Maximum risk per trade: 1%, so $10,000 × 1% = $100 of risk.
• Entry price: $50. Stop-loss: $47. Risk per share: $50 − $47 = $3.
• Position size: $100 ÷ $3 = 33 shares.

A small setback, not a disaster

In this example, the maximum planned loss is approximately $100 and the position size is 33 shares. Even if the trade fails, the overall account experiences only a small setback.

Choosing a stop-loss

A stop-loss should be placed where the trade idea is proven wrong, not where the loss feels comfortable. A properly placed stop reflects market structure and volatility. Good places for stops:

• Below a swing low: in an uptrend, a recent swing low often represents an area where buyers previously defended the stock. If price falls below that level, the bullish thesis may no longer be valid.
• Below support: a clear support level often forms beneath consolidations, ranges and chart patterns. A decisive break below support can signal that buyers have lost control.
• Below a moving average: some traders use major moving averages such as the 20-day, 50-day or 200-day average as reference points for stop placement.

ATR-based stops

The Average True Range (ATR) measures a stock's normal daily volatility. Instead of using a fixed dollar amount, the stop is based on the stock's typical movement. ATR-based stops help avoid being stopped out by ordinary market noise. For example:

• Entry: $100
• ATR: $3
• Stop: 2 ATR below entry, so $100 − ($3 × 2) = $94

Don't place stops arbitrarily

The market doesn't know how much you're willing to lose. The stop should reflect the chart and the original trade idea. A stop should never be based solely on:

• "I'm only willing to lose $50."
• "10% sounds reasonable."
• "This feels far enough away."

Don't move stops further away

One of the most damaging habits is moving a stop after entering a trade to avoid taking a loss. This turns a planned loss into an uncontrolled one. Accepting small losses is part of successful investing and trading. For example:

• Stop at $47
• Price reaches $47
• Stop moved to $45
• Then to $42

Understanding reward-to-risk

Every trade should offer enough potential reward to justify the risk being taken. The formula is: reward-to-risk ratio = potential gain ÷ potential loss. For example:

• Entry: $50. Target: $58. Stop: $46.
• Potential reward: $58 − $50 = $8.
• Potential risk: $50 − $46 = $4.
• Reward-to-risk ratio: $8 ÷ $4 = 2:1, so you're risking $1 to potentially earn $2.

Why reward-to-risk matters

You do not need a high win rate if your winners are larger than your losers. For a 2:1 reward-to-risk ratio, with an average winner of +$200 and an average loser of −$100, over 100 trades:

• 40 wins = +$8,000
• 60 losses = −$6,000
• Net result: +$2,000

Expectancy over win rate

Even with only a 40% win rate, the strategy remains profitable. This demonstrates why professional traders focus on expectancy rather than trying to win every trade.

When to skip a trade

Some opportunities look attractive but offer poor reward relative to risk. Patience is a risk-management tool, and sometimes the best trade is the one you don't take. Consider passing on a trade when:

• The stop needs to be very wide.
• The target is too close.
• The reward-to-risk ratio is unfavorable.
• Market conditions are uncertain.
• The setup doesn't clearly fit your plan.

The role of position sizing in survival

Position sizing protects you from both bad trades and bad luck. The purpose of position sizing is to ensure that losing streaks are frustrating, not devastating. The difference is enormous:

• Risking 10% per trade, five losing trades in a row leave your account down roughly 41%.
• Risking 1% per trade, five losing trades in a row leave your account down only about 5%.

The bottom line

Position sizing and stop-losses are the foundation of long-term success. A trader who consistently controls risk can survive mistakes, learn from them, and remain in the game long enough for skill and experience to compound. Remember the sequence:

• Identify the setup.
• Determine where the idea is invalid.
• Place the stop-loss.
• Calculate the risk per share.
• Size the position accordingly.
• Evaluate the reward-to-risk ratio.

How little you lose

Great traders are not defined by how much they make when they're right. They're defined by how little they lose when they're wrong.