What is Portfolio Diversification?
Portfolio diversification is spreading your investments across different asset classes (stocks, bonds, real estate, commodities) so that losses in one area are offset by gains elsewhere. It's a core principle of risk management.
Diversification is holding a mix of assets to reduce overall portfolio risk — if one asset falls, others may rise, smoothing returns. The rule: don't put all eggs in one basket.
- •80% single stock
- •20% cash
- •Volatility: ±40% per year
- •One bad news → major loss
- •40% stocks
- •30% bonds
- •20% real estate
- •10% cash
- •Volatility: ±15% per year
- •Losses spread, easier to ride out
Step-by-step worked examples
An investor has €100k: €80k in one tech stock and €20k in cash. The tech stock crashes 50%. What is the portfolio loss?
Concentrated loss = €80k × 0.50 = €40k loss. New portfolio value = €100k − €40k = €60k. Portfolio loss % = 40%. One stock bet = catastrophic risk.
The same €100k split: €40k stocks, €30k bonds, €20k real estate, €10k cash. Stocks fall 50%, bonds rise 5%, real estate flat, cash unchanged. What is the result?
Stocks: €40k × (1 − 0.50) = €20k. Bonds: €30k × 1.05 = €31.5k. Real estate: €20k × 1.00 = €20k. Cash: €10k. New total = €20k + €31.5k + €20k + €10k = €81.5k. Portfolio loss = €18.5k or 18.5% (much smaller!).
A portfolio is worth €200k. Stocks are 50%, Bonds 30%, Real estate 20%. Stock market rises 20%, bonds 2%, real estate 5%. Rebalance. What allocation now?
Stocks: €100k × 1.20 = €120k. Bonds: €60k × 1.02 = €61.2k. Real estate: €40k × 1.05 = €42k. New total = €223.2k. Stocks % = €120k / €223.2k = 53.7% (aim: 50%, rebalance). Sell €8.4k stocks → buy bonds/real estate to return to 50/30/20.
Flashcards
Quick quiz
Q1.What is the main goal of diversification?
Q2.Which portfolio is better diversified?
Q3.What is correlation in investing?
Q4.When should you rebalance your portfolio?
The full card deck, worked steps and AI-tutor support for “What is Portfolio Diversification?” are in Notek — study by hand before your exam.
Common mistakes
Owning 10 tech stocks is diversification. — Correct: All in one sector = high correlation. True diversification spans sectors and asset classes.
A diversified portfolio never loses money. — Correct: In market crashes, all assets may fall; diversification just reduces the loss.
Rebalancing is not necessary. — Correct: Rebalancing locks in gains, prevents over-concentration, and maintains your risk level.
Only stock investors need diversification. — Correct: All portfolios — bonds, real estate, cash — benefit from diversification across types.
FAQ
What is the ideal asset allocation?
It depends on your age, risk tolerance, and goals. Young investors (50/50+ stocks/bonds); older investors (40/60 or 30/70). Rules of thumb: 'Your age in bonds,' or target-date funds that adjust over time.
Is buying a diversified index fund enough?
A total stock index fund diversifies within stocks, but mixing stocks + bonds + real estate is broader diversification. Index funds are easy and cost-effective for beginners.
How many holdings do I need?
Research suggests 15–25 holdings eliminate most risk; beyond that, marginal benefit. Index funds with 500+ holdings are over-diversified.
Should I diversify internationally?
Yes — global diversification reduces home-country risk. Aim for 20–40% in non-US markets (developed + emerging). Currency risk is a trade-off.