Why this matters for beginners
Beginners often put too much into one exciting name. A single bad outcome then dominates the entire portfolio's result.
Main explanation
Position size is the percentage of your total portfolio held in one investment. A €1,000 position in a €10,000 portfolio is a 10% position.
A common beginner-friendly guideline is to keep single-stock positions small, often well under 10% each, so no single company can blow up your plan.
Broad ETFs can responsibly be larger positions because they already hold many companies inside them. A single stock is a concentrated bet on one outcome.
Position sizing is also about emotion: a position you can't sleep with is too big, even if the math 'works'.
Example using a real company
Think of an investor with 60% of their portfolio in one stock that drops 50%. Their whole portfolio drops 30% from one company's bad year. Position sizing is what prevents that.
- →A 3% position in a single stock that goes to zero costs the portfolio 3%. A 30% position in the same stock costs 30%.
- →Owning an S&P 500 ETF as a 60% position is very different from owning a single tech name as a 60% position.
Common beginner mistakes
- ✕Putting most of the portfolio into one favorite stock.
- ✕Adding to a losing position just because it's cheaper now, with no plan.
- ✕Not knowing your current position sizes as percentages.
Key terms
- Position size
- How much of your portfolio is in a single investment.
- Concentration risk
- The risk of having too much in one stock, sector, or theme.
- Rebalancing
- Adjusting positions back toward your target sizes.
Key takeaways
- 01Single-stock positions are usually best kept small.
- 02Position size controls how badly one mistake can hurt you.
- 03Know your sizes as percentages, not just euro amounts.
Check yourself
- 01A larger position in a single stock generally increases concentration risk.
- 02A 50% position in one stock is generally appropriate for a beginner.
Try the concept on a real company
Compare a single volatile stock (NVDA or TSLA) with a broad ETF (VOO) in the Analyzer. Notice how the risks for the single name are concentrated, exactly why position sizing matters.
Educational examples only. Not buy or sell recommendations.