回購公告是買入訊號嗎？追蹤 430 宗近期公告並與 SPY 比較

A buyback announcement reads like a company putting its own money behind its shares. I checked what actually followed recent ones: the first verified buyback announcement from each of 430 US-listed companies between July 2025 and June 2026, taken from the company's own SEC filings, with each stock measured against SPY over the same dates.

The 5- and 20-session rows cover 431 companies; one hadn't yet traded 63 sessions after its announcement.

Five findings

1. There's a small, uneven pop. The average stock beat SPY by 1.5 points over five sessions and 1.8 over 20. The typical stock did about half that, and barely more than half of them beat the index at all.

2. By three months the typical stock lags. After 63 sessions the median stock trailed SPY by 0.92 points and only 206 of 430 beat it.

3. One stock carries the average. A single company gained more than 300% against SPY in 63 sessions, which alone adds about 0.8 points to the mean. Trimming the top and bottom 5% cuts the 63-session mean from 2.00% to 0.66%; the median stays negative.

4. The median's confidence interval crosses zero every time. Bootstrapped 10,000 times, the median excess return's 95% interval was -0.01% to 1.68% at five sessions, -0.45% to 2.57% at 20 and -2.70% to 1.06% at 63. The mean's interval excludes zero at five and 20 sessions, which is the honest summary: a basket reacts, a single pick is a coin flip.

5. Authorization isn't purchase. A board authorization is a ceiling, not an obligation. Older research found the operating improvement after an announcement concentrated in companies that actually bought shares in the same quarter, and a study of 1994 to 2014 announcements found the long-run drift much weaker after the early years.

The traps I hit

• No hindsight from late filings. An event counted only if the filing stated the announcement date and arrived within 14 days of it. Otherwise a 10-Q mentioning an old program months later sneaks information into the past.
• One event per company. Serial announcers would otherwise dominate the sample.
• Exact listings and split-safe windows. Each ticker resolved to its exact listed security, only traded closes with volume were used, and no window crosses a stock split.
• Start before the news. Returns run from the last close before the announcement date, because day-level dates can't tell a before-open release from an after-close one.
• Report the median. With one +300% outlier in 430 stocks, the mean describes a basket you'd never hold.

What to check instead of the headline

• How big is the authorization against the market value?
• Did the company actually buy shares in the following quarters?
• Is the diluted share count falling, or are buybacks just offsetting stock compensation?
• Is it paid from free cash flow or new debt, and at what valuation?

With the Equibles MCP server connected to Claude or ChatGPT, a prompt like "Using Equibles, show Apple's buyback authorizations since 2022, how much it actually spent each year, and its diluted share count over the same period" answers the second and third questions for one company.

The full study has the charts, the bootstrap table and the literature it builds on: What Happens After Stock Buyback Announcements? Evidence From 430 Companies.