Short answer: the calendar mattered more than who bought. Insider purchases filed in October, November and December beat the S&P 500 over the next 90 days 53% of the time (3,694 cases since 2020). Purchases filed from January to April did so only 39% of the time (5,479 cases). Insider buys overall: 45.8%.
That's a bigger gap than anything we found for CEO buys, big buys or cluster buys. And unlike most patterns, it held up when we split the data in two.
Month by month
Share of insider buys that beat the S&P 500 over the 90 days after the filing:
| Month filed | Cases | Beat the S&P 500 | Median vs. S&P 500 |
|---|---|---|---|
| January | 704 | 38.4% | −3.9 pts |
| February | 1,325 | 37.0% | −4.5 pts |
| March | 2,585 | 39.6% | −4.5 pts |
| April | 865 | 39.7% | −3.7 pts |
| May | 2,479 | 49.6% | −0.1 pts |
| June | 1,615 | 46.6% | −1.4 pts |
| July | 623 | 43.0% | −2.4 pts |
| August | 1,769 | 44.9% | −1.9 pts |
| September | 1,240 | 49.1% | −0.3 pts |
| October | 617 | 54.0% | +1.1 pts |
| November | 1,599 | 54.3% | +1.8 pts |
| December | 1,478 | 51.0% | +0.5 pts |
October, November and December are the only months where the typical buy actually beat the market.
Did it hold up?
A pattern found by slicing data many ways can easily be luck, so we check every finding in two separate periods: buys before April 2023 and buys since.
| Before Apr 2023 | Since Apr 2023 | |
|---|---|---|
| All insider buys | 47.2% | 44.5% |
| October–December buys | 56.9% | 49.4% |
| January–April buys | 40.3% | 37.0% |
Late-year buys beat the average in both periods (by 9.7 and 4.9 points), and early-year buys trailed it in both (by 6.9 and 7.5 points). The edge was smaller in recent years, which is worth keeping in mind.
Why might this happen?
We can measure the pattern but not prove the cause. Two possible explanations:
- Tax-loss season. Investors often sell losing stocks late in the year to book tax losses, which can push some smaller stocks lower than they deserve. Insiders buying into that selling may be getting a better price.
- What the 90 days cover. A buy filed in November is measured through February; a buy filed in February is measured through May. Small stocks have historically had a tendency to do relatively well around the turn of the year, which would help late-year buys.
Either way, it's a pattern in history, not a rule. Three or four years of data per month is not a lot.
Check it yourself
- Pick any month (and add other filters) in the Backtester. It shows the before/after-2023 split for whatever you choose.
- Quick answers to "is there a best month?" and other questions are on Ask the filings.
- See this week's insider buys on Latest filings.
Data: SEC Form 4 filings and SEC insider transaction data sets, 2020 to October 2026 (buys whose 90 days had finished). Month = month the last filing in a buy event became public. Price-only returns, no trading costs; delisted stocks often drop out. History, not a prediction, and not investment advice.