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What your portfolio does in a crash, before one happens.

Pick a crash the market already lived through and watch the book you hold today fall through it: the worst session, the bottom, and how long it stayed under water.

  • real closes, day by day
  • a sample book runs first
  • no account

Feb 19, 2020 → Sep 4, 2020

COVID crash

The world shut down and the market repriced everything in five weeks — the fastest fall of its size on record, and the fastest recovery.

Your book

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Feb 19, 2020 — the last record high before the fall

-30%-20%-10%
peak
FebMarAprMayJunJulAugSep
s&p 500waiting for your holdings

Worst session

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Bottom

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Under water

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vs s&p 500

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Looking for your holdings…

> your book

reading your holdings

The chamber uses what you hold now and what those things did back then. It never asks when you bought — so it works the first time, with nothing imported.

Track this book in the terminal

Closes from Yahoo Finance for your holdings, and for the S&P 500 the window is measured against. Your book is carried through at today’s weights, so the chamber measures the portfolio you hold now, not the one you held then. Holdings that had not started trading are left out of the line and named above.

Track the book, not just the crash.Import it and the terminal replays these windows on your real lots, alongside your live risk, your drawdown and a daily briefing.Check how concentrated it is firstImport it, free

How to read it

The bottomdeepest point vs the day it started
The number that decides whether you sell: not the loss you took, the loss you were looking at.
The worst sessionlargest single move down
One day inside the fall, the one people remember and usually the one they acted on.
Under waterfrom the peak to the day back above it
How long the decision had to hold. A fall you sit through costs nothing; the waiting is the price.

Each window runs from a peak to the day the index got back above it, so every one contains its own recovery.

What it does not do

It replays, it does not forecast. The weights you hold today go through a window that already happened, as if you had bought nothing and sold nothing on the way.

Real portfolios are not held that still: people add, trim and panic. What it gives you is the shape of the risk already in the book, against a crash the market actually delivered.

Questions

Do I need an account to run the crash test?

No. Paste your holdings, or run the sample book, and the chamber replays immediately. The only thing sent to a server is the list of symbols, to fetch their closes for that window.

Does this predict the next crash?

No, and nothing can. The crash test replays windows that already happened, using the closes those holdings actually printed. It answers "what would this book have done in that", not "what happens next".

Why does it not ask when I bought?

Because it measures the portfolio you hold now. The chamber takes today's weights and carries them through a dated window, so a buy date would not change the answer. It also means the test works the first time, before any import.

Why is 2008 not one of the chambers?

The S&P 500 took five and a half years to get back above its 2007 high, and a large share of what people hold today was not listed yet. A window that long would measure the survivors rather than the crash. Every chamber here contains its own recovery, so the clock always has a day to count to.

What happens to a holding that did not exist back then?

It is left out of the line and named on screen, and the chamber says what share of the book the line actually speaks for. Nothing is quietly filled in with a proxy.

Where do the numbers come from?

Daily closes from Yahoo Finance for your holdings and for the S&P 500, gold and the STOXX 600, plus Brent from FRED. The comparator closes are baked into the page, so the same window always reads the same way.

A replay of past windows, not a forecast. Not investment advice.

Portfolio Crash Test: Your Holdings Through 2020–2024