Recency Bias and the Cost of Timing the Market

Say you have $2,000 in a stock fund. After several sharp market moves, you want to move it to cash and come back “when things feel calmer.”

You can name the exit. You cannot name the return.

Then you see a chart showing the cost of missing the market's best days. It seems to settle the argument. But what if you had missed the worst days?

Taking money out for a bill is a different decision. That money has a spending deadline, regardless of where you think the market is heading.

The latest stretch starts to look normal

After a strong run, more gains feel natural. After a bad stretch, more losses feel inevitable.

An anchor can pull you toward an old purchase price. Recency bias gives recent experience too much weight.

Return extrapolation is projecting a recent run of returns into the future: prices have been rising, so you expect them to keep rising. A string of losses can feed the opposite forecast.

Robin Greenwood and Andrei Shleifer's 2014 study examined six sources of investor expectations covering different parts of 1963–2011. Higher past returns and market levels went with greater optimism about future returns.

The finding describes investors' expectations; it does not tell you which way the next return will go.

Here, discretionary market timing means changing how much you have invested because you expect the market to rise or fall in the near term. Scheduled saving, a bill withdrawal or a rule-based rebalance can change your holdings without making that forecast.

Timing adds a forecast to the decision.

What skipping one day does

Give that $2,000 a made-up six-day path, invested before day 1: −10%, +8%, −8%, +10%, +1%, +1%.

Leave out distributions, deposits, withdrawals, fees and taxes; price and total returns match here. The first day's 10% fall leaves $1,800. The next day's 8% gain applies to that smaller balance, bringing it to $1,944.

To skip the best day, replace day 4's 1.10 with 1. To skip the worst, replace day 1's 0.90 with 1 instead. Everything else stays the same.

The middle bar barely clears the $2,000 starting line. Missing the best day produces a loss; missing the worst produces a gain. The calculation changes sides when you change the day you leave out.

What this comparison cannot prove

“Best” and “worst” are labels you attach after the days have happened. The arithmetic hands you the right day to skip. A trading decision has to find it beforehand.

Volatility clustering means large moves tend to occur close together, whether up or down. Quiet stretches can cluster too. A frightening stretch can contain both sharp losses and sharp gains. Clustering describes the size of moves, not tomorrow's direction.

Vanguard's 2025 analysis shows that clustering in S&P 500 daily price returns during 2020–2024. Its missed-best-days example uses a different series: S&P 500 total returns from 1988–2024.

These bars show what a missed day costs or saves. Neither outcome settles whether a timing strategy works. A fair test starts with rules set before the outcomes, then measures all gains and losses after trading costs and any taxes. It must count wrong calls as well as right ones.

A bill and a forecast need different plans

In case A, you need $200 from investments for a bill due in 30 days. In case B, you want the $2,000 in cash until the market feels safe. Before reading the answers, decide what changed and which case needs a condition for returning.

For A, start with your existing cash arrangements and selling plan. Money spent on the bill may never be reinvested. Paying a bill does not require an opinion about stocks.

For B, “feels safe” can keep moving. If prices fall further, buying may feel even more dangerous. If they rise, returning may feel like chasing a rebound. Either outcome can become a reason to keep waiting.

Getting out is only half a timing decision. Before the trade, both sides need an explanation:

• Exit trigger. The event that would cause you to leave.
• Return trigger. A condition you could observe that would bring you back.
• Evidence. Results that support the rule after costs; confidence alone is not evidence.
• Reason to reconsider. What would show that your forecast was wrong.

A specific rule gives you something to test; it does not establish an advantage. If another loss would endanger necessary spending, that is a reason to revisit your investment policy. You have learned something about how much risk your money can bear, even if you learned it during a bad week.

For the opening $2,000 decision, you can already say: “This is a timing idea; I still lack a return trigger and evidence it would help.” Recognizing an unfinished trade is a useful answer.

The next lesson, fear and greed indicators, is an optional look at gauges that can feed a timing urge. For the core practice, continue to the investing journal and preserve the reason before the outcome.

In short

• Recent returns can shape expectations without making those expectations reliable.
• Skipping the best day hurts this calculation; skipping the worst day helps it. Both use hindsight.
• Large gains and losses can cluster; a bad day does not promise a rebound.
• A bill needs cash by a deadline. A temporary timing trade needs a return rule backed by evidence.