The crash test

How this is calculated

What it calculates

Not a formula in the strict sense but a behaviour test: you live through a randomly chosen crash month by month and decide each time. Hold, buy more or sell. At the end you see what your decisions cost or earned you.

Your inputs

• Starting capital: the amount you start with.
• Your decisions: one click per month.

How it works

There are five paths, modelled on the crashes of 1929, 2000, 2008, 2020 and a major crypto crash. Each path consists of a few anchor points (month and price index, starting at 100); the months in between are joined in a straight line. A small, regular wobble of at most about ±3 points keeps the line from looking smooth. The paths are stylized, not exact historical monthly data.

Units at the start = starting capital ÷ 100
Portfolio value = units × current index
From the peak = current index ÷ highest level so far − 1

Buy more invests an extra 20% of your starting capital at the current level, so you get more units. Sell freezes your value; the calculator compares it with what you would have had by holding to the last month. No fees, dividends or inflation.

What the result means

The difference shows what selling in a panic costs: a paper loss becomes permanent, while in many of these paths the market later recovers, but not in all of them, and not always quickly.

Example

€10,000 of starting capital buys 100 units. If the index falls to 50, your portfolio shows €5,000 (−50% from the peak). If you sell there and the path ends at 96, holding would have left you with €9,600: a €4,600 difference.