Every S&P 500 drawdown of 10% or more since 1928

Depth on its own is a headline. Depth next to recovery time is a plan. A 20% decline — the median in this table — is unpleasant and, on the historical record, over in a matter of months. The declines that reshaped how a generation invested are the handful in the top rows, where the recovery is measured in years and in one case in decades.

The relationship between the two columns is closer than most other things in market history. Recovery time tracks depth far more tightly than it tracks the decade, the cause, or the policy response — which is the practical argument for caring about the depth of a decline above almost anything else. It is also why the required-gain arithmetic is worth internalising: the deeper the hole, the more of the subsequent bull market is spent simply getting back to a level that had already been reached once.

Two definitional points, because they are where published figures disagree. These are closing levels, not intraday: an intraday series shows slightly deeper troughs, most visibly in October 1987. And the page does not use a 20% threshold to decide what counts — every decline of 10% or more is listed with its depth, so any cutoff you prefer can be applied by eye. The conventional bear-market line is arbitrary, and the table makes it obvious how many declines stopped a percentage point or two short of it.

One thing the table cannot show: how any of these felt while they were happening. Every row bottomed, and the bottom is only identifiable afterwards. At the trough of each of them the available evidence pointed down, which is why "it always recovers" is true of this table and useless as a decision rule at the moment it is needed.