What Is a Bear Market?

Michael Whitman · Trading since 2017, full-time since 2020 · YouTube creator, 137K subscribers · Published 2026-09-14 · Updated 2026-10-19

A bear market is a label applied to a decline after the decline has reached a size somebody once decided was significant. Understanding how arbitrary that threshold is makes the term far more useful.

How it works

The conventional threshold is a 20% fall from a recent high. Below that it is called a correction; past it, a bear market.

There is nothing behind the number. Twenty percent was not derived from any study of market behavior — it is a round figure that became standard through repetition in financial journalism.

Which means the label tells you about magnitude and nothing about cause, duration or what comes next. A 19% fall and a 21% fall are treated as different categories and are the same event.

The recovery arithmetic

Losses and gains are not symmetric, because the base changes. Falling 20% leaves 80; getting back to 100 from 80 requires a gain of 25%, not 20%.

And it steepens. Down 50% needs 100%. Down 70% needs 233%. The deeper the hole, the more disproportionate the climb out, which is the same arithmetic risk of ruin works through.

This is why avoiding large losses matters more than capturing large gains. Not as a temperament preference — as arithmetic. A portfolio that never falls 50% never needs to double to stand still.

A worked example

Take the deepest bear market in the S&P 500 since 1950. The index closed at 1,565.15 on 9 October 2007 and at 676.53 on 9 March 2009, a fall of 56.8%, and it did not close above the 2007 level again until 28 March 2013.

Now apply the recovery arithmetic to that bottom. Climbing from 676.53 back to 1,565.15 needed a gain of about 131% — more than twice the size of the fall that caused it.

Being underwater is also the normal state, not a bear-market special. On 93% of the index’s trading days since 1950 it closed below a record it had already set.

And the length of the wait is the part that breaks plans. A decline recovered quickly is survivable on resolve alone; the January 1973 peak was not regained until July 1980, 1,897 trading days later, which outlasts most people’s conviction and is why positions get abandoned at the bottom rather than at the top.

You cannot time either end

The start is invisible. Every bear market began as an ordinary decline that did not stop, and every ordinary decline that did stop looked identical at the time.

The bottom is only visible afterwards. Up days are nearly as common as down days — 53.1% of the index’s sessions since 1950 closed higher — so a cluster of them, which is what a bottom feels like, turns up again and again inside declines that still have far to go.

Which is what makes a bear market rally so convincing, and why it gets its own term.

The original data

Of the 24,971 trading and investing videos measured for this site, 23 have “bear market” in the title, from 17 channels, at a median of 11,149 views.

The price record tells the story the attention misses. The S&P 500 closed below a prior record on 93% of its trading days from 1950 to 2026 and had 68 separate stretches closing 5% or more under one, so a plan built on the assumption that declines are brief interruptions is planning for the rare days at a new high.

Where the twenty percent came from

Nobody is quite sure, which is itself informative. The threshold appears in financial journalism through the twentieth century without any founding study behind it, and it survives because it is round, memorable and produces a satisfying number of events per decade.

A different threshold would produce a different history. At 15% there are far more bear markets; at 30% there are very few. The events did not change — the categorization did, and every claim about how often bear markets occur is really a claim about where somebody drew a line.

This matters when a statistic is quoted at you. “The average bear market lasts X months” is computed over a set of episodes selected by the 20% rule, so the average is a property of the rule as much as of markets.

And it explains why the label feels arbitrary in practice. A portfolio down 19% and one down 21% are in the same situation, and only one of them is in a bear market according to the convention.

How this connects

Asset allocation decides how a bear market feels before it begins. The split between shares, bonds and cash sets the depth of a portfolio’s decline far more reliably than any decision taken during one.

An emergency fund keeps the plan intact. Money held outside the market means nobody has to sell holdings at depressed prices to cover a bill.

Market timing is the tempting alternative, and it needs both the exit and the re-entry to be right, which is two hard calls rather than one.

Dividend reinvestment works quietly in the other direction. Payments reinvested during a decline buy more shares at lower prices, which shortens the recovery the arithmetic demands.

Implied volatility tends to rise as prices fall, so option protection is cheapest before a bear market and most expensive in the middle of one.

The ways to profit from a fall have their own traps. Short selling faces open-ended losses in a sharp rally, and an inverse ETF that resets daily drifts away from the index over long holding periods.

And for retirees the danger is sequence. A safe withdrawal rate is set with bad early years in mind, because selling to fund withdrawals near a bottom turns a temporary decline into a permanent one.

The death cross printed inside every S&P 500 decline of 20% or more since 1950, usually after the index was already well off its high.

When it fails

The characteristic failure is selling once the label is applied. The 20% threshold is crossed, the media begins using the term, and the decision to reduce is made at a point defined by an arbitrary round number rather than by anything about the position. The selling happens after the fall that triggered the label, into the conditions where the spread is widest, and the buyer is somebody who did not organize their decisions around a journalistic convention.

A second failure is waiting for an official end. There is no announcement, and by the time the recovery is obvious it is priced.

A third is assuming bear markets are brief. Some are; others are not, and the index took about 5.5 years after its October 2007 peak to close above it again.

A fourth is judging a strategy by its behavior in one. A single decline is one observation, and the sequence matters more than the average.

The question: Down twenty percent. Buy or wait?

And a fifth is confusing a bear market with a permanent loss. A decline in a diversified holding is recoverable; a decline in one company may not be, which is the distinction business risk covers.

Related

Bull market covers the mirror label and the same identification problem. Risk of ruin covers the recovery arithmetic in full. And volatility covers the bar sizes a decline is built from.

This page is educational, not financial advice. Test every idea on your own charts before risking money.