Open this calculator on its own page
📏 Position Size Calculator
A stop distance and a fraction of the account give you a share count. Lesson 20 shows the fraction decides your depth, not your return.
💡 Quick Insight
Professional traders risk the same PERCENTAGE on every trade, not the same dollar amount. This ensures your risk stays proportional to your account size as it grows or shrinks.
Why Position Sizing is Everything
Most traders lose not because they're wrong, but because they're sized wrong. You can be right most of the time and still blow up if you risk too much when you're wrong.
⚠️ The Asymmetry of Losses
A 50% loss requires a 100% gain to recover. This mathematical reality is why risk management isn't optional. It's survival.
- Down 20%? Need +25% to recover
- Down 30%? Need +43% to recover
- Down 50%? Need +100% to recover
The Reality Check
| Risk Per Trade | 5 Consecutive Losses | 10 Consecutive Losses | Outcome |
|---|---|---|---|
| 1% | -5% | -10% | Recoverable |
| 2% | -10% | -18% | Challenging |
| 5% | -23% | -40% | Career-ending |
| 10% | -41% | -65% | Account death |
✓ Real Example
$10,000 account, risking 2% = $200 risk
Entry at $50, stop at $48 = $2 risk per share = 100 shares
Same trader at 5% risk = 250 shares. Feels like "only 3% more risk" but creates 150% bigger position.
Professional Guidelines
- Learning Phase: Risk 0.5-1% per trade
- Profitable Trader: Risk 1-2% per trade
- Experienced Pro: Risk 2-3% per trade (multi-year track record only)
- Red Flag: Anyone suggesting 5%+ is selling dreams, not strategies
Common Position Sizing Mistakes
Risking the Same Dollar Amount
Trader always risks $500 per trade. Account starts at $50,000, shrinks to $30,000. Still risking $500.
Problem: $500 was 1% at $50k, now it's 1.67% at $30k. Risk increases as account shrinks = death spiral.
Counting Position SIZE Instead of Position RISK
"I always buy 100 shares" sounds consistent, but volatility changes everything.
Example: 100 shares of Tesla (4% ATR) = completely different risk than 100 shares of Apple (1% ATR).
Not Accounting for Gap Risk
Stop at $95, but stock gaps down to $90 on earnings. You planned for $5 risk, you got $10 risk.
📖 Learn More
For deep dive into position sizing science, see Lesson 20: Position Sizing
Professional Position Sizing Tips
Volatility-Adjusted Sizing
Don't just calculate shares, adjust for ATR (Average True Range).
Formula: Position Size = (Account × Risk%) / (ATR × Multiplier)
Higher volatility = automatically smaller position. Risk stays constant.
Portfolio Heat Management
Individual trade risk is only part of the equation. Track TOTAL exposure.
Example: 5 open positions at 1% each = 5% total portfolio heat
Professionals cap total heat at 6-8%. Above that, stop taking new trades.
Scale Based on Conviction
A-grade setups: Full position (2%)
B-grade setups: Half position (1%)
C-grade setups: Quarter position (0.5%)
This allows you to stay in the game while allocating more capital to your best ideas.
The 2% Rule
Never risk more than 2% on any single trade, no matter how "sure" you are.
Why? Even 90% probability trades lose 10% of the time. If you bet 10% on "sure things," you'll eventually hit that 10% and crater your account.
🎯 Kelly Criterion
Advanced position sizing uses the Kelly Criterion formula based on your edge and payoff ratio.
Most pros use 1/4 Kelly (fractional Kelly) to account for estimation errors and reduce volatility.