Time in the market, not timing it

Market timing is the attempt to sell before falls and buy before rises. The intuition is obvious and the appeal is enormous. The evidence against it is unusually clean, because the argument does not require you to believe timing is impossible in principle. It only requires you to look at where the returns actually arrive.

The best-days data

Hartford Funds maintains a long-running study of this, measured on the S&P 500. Over the 30 years from 1 July 1995 to 30 June 2025, their figures show an average annual return of 8.4% for an investor who stayed fully invested the entire period. Miss the 30 best days and that falls to 2.1% a year, which was below the 2.5% average inflation rate over the same period. Missing the 10 best days cut returns roughly in half.

Put that in dollars on a single $10,000 investment left alone for the 30 years:

How few days that is

This is the part worth sitting with. A 30-year period contains roughly 7,560 trading days. Thirty days is about 0.4% of them. Ten days is about 0.13%.

So an investor who was out of the market for one eighth of one percent of the available days, and fully invested for the other 99.87%, halved their return. Not because they were wrong for most of the time, but because they were absent on a handful of specific dates.

That clustering is what makes timing structurally hard rather than merely difficult. It is not enough to be right about the fall. You have to be right about the fall and right about the recovery, and the recovery announces itself only afterwards. A person who sold because things looked bad is, by construction, standing outside during precisely the fortnight the returns are delivered.

The behaviour this produces

Nobody sets out to time the market. They do it one reasonable decision at a time.

And the reasons are never flimsy. That is the part worth sitting with. Markets do not fall for no reason, they fall alongside genuinely frightening and correctly reported events. March 2020: a global pandemic, borders closed, nobody able to say how long any of it would last. 2022: a war in Europe, an energy shock and the fastest interest rate rises in a generation. 2008: institutions that had stood for a century failing inside a fortnight. Every one of those was a real crisis. Every one of them was also a terrible moment to sell. The reasons are real. They are simply not predictive.

1. The market falls sharply. The reporting is relentless and the reasons sound convincing, because during a fall the reasons always sound convincing.
2. Selling and waiting for stability feels prudent rather than panicked.
3. The market recovers before it feels safe, because that is when recoveries happen.
4. Buying back now means buying higher than you sold, which feels like locking in the mistake, so you wait for a dip.
5. The dip does not arrive at the level you want. You re-enter much later, or not at all.

The loss is not the fall. The fall was recovered. The loss is the absence during the recovery.

What this does and does not argue

It does not argue that markets always go up, that any individual company is safe, or that a 30-year US figure is a forecast. It argues something narrower and more durable: returns arrive unpredictably and in concentrated bursts, so being present is a precondition, and the most common way to be absent is to sell during a fall.

The honest caveat on the data: this is the S&P 500, the world's most studied and one of its best-performing markets over that window, and past periods are not a promise. The clustering result, however, shows up across markets and periods and it is the part that matters here.

What to do with this

• Decide your contributions in advance and automate them. A decision made once is not remade every time the news is bad.
• Do not invest money you will need inside five years. Then you are never forced to sell at the wrong moment, which is the actual protection. Your emergency fund (cash set aside for when things go wrong) is what makes the rule hold: it covers the burst pipe so the portfolio never has to.
• Treat waiting for a better entry point as timing. It is the same decision, made with the same information, wearing a more patient face.
• Check your balance less often. Checking daily does not improve a 30-year outcome and reliably makes selling more tempting.

The next lesson deals with the other half of this: why volatility is not the same as loss, and why your time horizon changes what a fall actually means for you.