Applying history: stress-testing your own plan
Build historical-style crisis scenarios and test your own portfolio, income and cash reserve against them, then turn the results into written rules.
What you will learn
- What a personal stress test is and which three areas it must cover
- How to build a small scenario table from the crises in this course
- How to calculate euro losses, drawdowns and months of cash cover
- How to turn a failed test into concrete changes and written rules
Explanation
Emergency funds and rebalancing are covered in the personal finance and ETF courses; this lesson tests whether your whole plan survives a crisis.
What a stress test is
A stress test asks: "What happens to my money and my life if a severe but plausible crisis happens now?" Banks are required to run them; private investors rarely do. A personal stress test covers three areas:
- Portfolio: how much would each holding lose?
- Income: could you lose your job or customers at the same time? Crises hit jobs and markets together.
- Liquidity: could you pay your bills without selling investments at the low?
A scenario table
A historical scenario applies losses similar to a past crisis. A hypothetical scenario combines shocks that have not happened together yet. The table below uses round planning assumptions inspired by this course. They are not exact historical figures, and a future crisis can be worse.
| Scenario | Equities | High-quality government bonds | Crypto | Income |
|---|---|---|---|---|
| Severe banking crisis (2008-style) | −50% | +5% | −80% | Job loss possible |
| Fast shock (2020-style) | −35% | 0% | −50% | Short-time work possible |
| Euro-area stress (2011-style) | −30%; banks −60% | Weaker countries' bonds −40% | −50% | Regional job losses |
| Inflation shock (1920s/1970s-style) | Real losses | Real losses | Uncertain | Wages lag prices |
Questions to answer
- What is my loss in euros and percent? Could I live with it without selling?
- How many months of expenses does my cash cover?
- Are my job, my home and my investments all exposed to the same economy or employer? For many people in Germany, salary, property and a home-biased portfolio all depend on the German economy.
- Do I use any leverage that could force a sale?
Turning results into rules
Set a maximum acceptable drawdown before the test, for example 25%. If the scenario loss is larger, change the plan now: reduce the equity or crypto share, increase cash, remove leverage. Then write pre-commitment rules, such as "I rebalance when a weight drifts more than 10 percentage points", "I use no borrowed money", and "I do not sell because of a headline". Repeat the test once a year and after major life changes.
Worked example
Hypothetical example: a household has €80,000: a global equity ETF (exchange-traded fund) €48,000, a government bond fund €16,000, Tagesgeld (instant-access savings) €12,000 and crypto €4,000. Monthly expenses are €2,500. Scenario: severe banking crisis from the table. Fees, taxes and inflation are excluded.
- Equities: €48,000 × 0.50 = €24,000.
- Bonds: €16,000 × 1.05 = €16,800.
- Cash: €12,000 (no change in euros).
- Crypto: €4,000 × 0.20 = €800.
- Total: €24,000 + €16,800 + €12,000 + €800 = €53,600. Loss €26,400, or −33%.
- Cash cover: €12,000 ÷ €2,500 = 4.8 months.
- Add a six-month job loss, assuming income replacement of €1,000 per month: gap €1,500 × 6 = €9,000. Cash covers it, leaving €3,000, so no investments must be sold at the low.
Result: the plan survives this scenario. If the household's limit were 25%, it would need to reduce risk.
Common mistake
Practice activity
On paper: a hypothetical investor holds €30,000: equities €21,000, bonds €6,000, cash €3,000. Monthly expenses are €1,800. Maximum acceptable drawdown: 25%. Scenario: equities −45%, bonds +3%, cash 0%. (1) Calculate the new total, loss and drawdown. (2) How many months does the cash cover? (3) Does the plan pass? (4) Keeping cash at €3,000, what is the largest equity amount (the rest in bonds) that keeps the loss at or below 25%?
Show solution
(1) Equities €21,000 × 0.55 = €11,550; bonds €6,000 × 1.03 = €6,180; cash €3,000. Total €20,730. Loss €9,270, drawdown −30.9%.
(2) €3,000 ÷ €1,800 ≈ 1.7 months, which is thin.
(3) No: −30.9% is worse than the 25% limit, and cash cover is short.
(4) Maximum loss: 25% × €30,000 = €7,500. With equities E and bonds €27,000 − E, loss = 0.45E − 0.03(€27,000 − E) = 0.48E − €810. Set 0.48E − €810 = €7,500, so E ≈ €17,300. Move about €3,700 from equities to bonds; ideally also build more cash.
Limitations: real crises can produce larger losses, bond losses at the same time as equity losses, and different timings.
Key takeaways
- A personal stress test covers portfolio, income and liquidity together.
- Use round, severe scenarios inspired by history and remember the next crisis can be worse.
- Compare the result with a maximum drawdown you set in advance, and change the plan if it fails.
- Written rules made in calm times protect you from panic decisions in a crisis.
Next step
You have completed this course; continue with the course "Islamic Finance & Sharia-Compliant Investing" to learn how ethical and religious rules shape investment choices.
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