Published October 28, 2026 · by Troels Højbjerg, Founder
An insider buy is an officer, a director or a large owner buying shares of their own company with their own money. They have to report it to the SEC on a Form 4 within two business days.
I measured 6,802 such buys in US stocks from 2018 to 2026. Ninety days later the stocks were up 11.1% on average, 6.3 points more than the S&P 500 in the same windows. But only 50.4% of the buys beat the index. The average is pulled up by a small number of big winners. Across all 7,107 buys in the study the median buy beat its index by only 0.1 points.
That study counts from the closing price on the day the insider traded, before you could have known about it.
| Company value at the time of the buy | Buys | Points vs. the index after 90 days, average | Share that beat the index |
|---|---|---|---|
| Under about $0.75 billion | 765 | +23.4 | 53.5% |
| About $0.75 to $3.7 billion | 1,231 | +11.6 | 53.5% |
| About $3.7 to $15 billion | 1,132 | +4.8 | 54.5% |
| Over about $15 billion | 3,705 | +1.2 | 47.5% |
Source: my insider study, 7,107 buys 2018-2026, of which 6,802 in US stocks, each against its home index. The size groups are set in Danish kroner and converted at 6.72 kroner per dollar (October 28, 2026).
In the smallest companies insider buys beat the index by 23.4 points on average, yet only 53.5% of them beat it. In companies worth more than about $15 billion the lead was +1.2 points, and fewer than half of the buys (47.5%) beat the index.
I also measured it the way you would use it: starting three trading days after the trade, when the Form 4 is public, in the 199 US stocks on WallStreetBuys that I measured (median company value about $46 billion). The yardstick is the median of the same 199 stocks over the same 60 trading days.
| Trade | Cases (stock-days) | Points vs. the other stocks after 60 trading days, median | Share that beat them |
|---|---|---|---|
| Open-market buy | 2,147 | −1.1 | 47.0% |
| Two or more insiders buying the same day | 290 | −0.5 | 47.2% |
| Buys of $1 million or more | 159 | +1.2 | 51.6% |
| Open-market sale | 12,161 | +0.8 | 51.8% |
Source: my own calculation on SEC Form 4 open-market trades (codes P and S), January 2023 to July 2026, prices from our price database. Only stocks still listed today.
None of these differences is large enough to trade on. In these stocks an insider buy was not a signal on its own, and an insider sale was not a warning.
Insider buying mattered most in small US companies and little in large ones. Across 6,802 US insider buys, the stocks beat the S&P 500 by 6.3 points on average over 90 days, but only 50.4% of the buys beat it. In companies worth more than about $15 billion the lead shrank to +1.2 points. In the 199 stocks I measured from the day the trade was public, buys did 1.1 points worse than the other stocks in the median, and insider sales were no warning. So the size of the company mattered more than the buy itself. What I cannot tell you is why a particular insider bought; the filing does not say.
One thing to check: when you see an insider buy, look at the size of the company first. Over about $15 billion, the buy said little in my data.
The open-market insider trades in each company are on its stock page, free and with no sign-up. How Form 4 filings work and how I read them is under Insider trading.
Sometimes, and mostly in small companies. In my study of 6,802 US insider buys from 2018 to 2026, the stocks beat the S&P 500 by 6.3 points on average over 90 days, but only 50.4% of the buys beat the index: a few big winners carry the average. In the 199 US stocks I follow, buys that were already public did not beat the market.
Not in my data. In the 199 US stocks I measured, stocks that insiders had sold did about as well as the market over the next 60 trading days: a median of 0.8 points better, and 51.8% beat it. Insiders sell for many reasons, such as taxes, a house or spreading their wealth, so a sale says little on its own.
US insider trades are public: officers, directors and owners of more than 10% must file a Form 4 with the SEC within two business days. Each WallStreetBuys stock page shows the open-market insider trades in that company, and the page Insider trading explains how the filings work.
Read also: When to sell a stock · How to find undervalued stocks · Insider trading · Methodology
This is information, not individual investment advice. The numbers are our own calculations on market data and may contain errors. Past results are no guarantee of the future. You decide for yourself — and remember to spread your risk.