Position Sizing
How much you invest in each stock matters as much as which stocks you pick. Position sizing determines portfolio risk and return.
Even the best stock pick can hurt your portfolio if it's too large a position and goes wrong, or barely help if it's too small.
Why Position Sizing Matters
| Aspect | Impact |
|---|---|
| Sleep quality | Right size = less stress |
Key Principles
1. Bet Size vs Conviction
Match position size to conviction:
| Conviction | Position Size |
|---|---|
| Very high | 5-8% of portfolio |
| High | 3-5% of portfolio |
| Moderate | 1-3% of portfolio |
| Low | Avoid or minimal |
2. Never Bet the Farm
No single stock should dominate:
- Maximum single position: 10%
- Limits damage from single failure
- Even high-conviction bets can fail
If you can't sleep at night worrying about a position, it's too large. Reduce and breathe easier.
3. Scale With Time
Build positions gradually:
- Start with smaller allocation
- Add as thesis confirms
- Average down only with conviction
- Give first purchase time to prove
Position Sizing Approaches
Fixed Percentage
| Position # | Allocation |
|---|---|
| 1-5 positions | 5% each |
| 6-10 positions | 3% each |
| 11-20 positions | 2% each |
Simple but doesn't account for conviction.
Conviction-Weighted
| Tier | Conviction | Allocation Range |
|---|---|---|
| A | Highest | 5-8% |
| B | High | 3-5% |
| C | Moderate | 1-3% |
Total: Build portfolio respecting overall limits.
Kelly Criterion (Advanced)
Optimal Bet = (p × b - q) / b
Where:
- p = probability of winning
- q = probability of losing (1-p)
- b = win/loss ratio
Kelly criterion gives theoretical optimal bet, but it's often too aggressive. Many investors use "half Kelly" for safety.
Practical Guidelines
For New Investors
| Guideline | Reason |
|---|---|
| Start smaller | Room to add |
For Experienced Investors
| Guideline | Reason |
|---|---|
| Can go 8-10% for best ideas | Higher conviction |
| May run concentrated (10-15 stocks) | Better research coverage |
| Still respect max limits | Even experts are wrong |
Adjusting Position Size
Increase When:
- Thesis strengthening
- Price falls (if fundamentals intact)
- Higher conviction after more research
Decrease When:
- Thesis weakening
- Position grown too large (from price gains)
- Need to rebalance
- Better opportunity elsewhere
Stock-Specific Considerations
| Factor | Position Size Impact |
|---|---|
| Turnaround situation | Smaller due to risk |
Small-cap stocks with low liquidity are tricky. You may not be able to exit a large position when needed.
Portfolio Constraints
| Constraint | Example |
|---|---|
| Liquidity | Enough to exit in week |
Common Mistakes
| Mistake | Problem |
|---|---|
| Over-allocating to new positions | Not time-tested |
Key Takeaways
- Position size affects returns as much as stock selection
- Match size to conviction level
- No single stock exceeds 5-10% of portfolio
- Build positions gradually
- Adjust as thesis evolves
Next: When and how should you actually buy?
Sources & Disclaimer
- CFA Institute - Equity Asset Valuation
- NCFM Fundamental Analysis Module
Note: Any benchmarks (e.g., "Good ROE is > 20%", or specific P/E ranges) are simplified industry heuristics for educational purposes. True evaluation depends on specific industry context, market cycles, and individual company circumstances.