Quick definition Earnings drift is the slow upward movement of stock prices after beating earnings expectations, and slow downward movement after missing expectations. What it is When earnings are announced, prices initially react. But if the reaction is too small, prices drift in the direction of the surprise for days or weeks afterward. Earnings drift is a specific case of post-announcement drift focused on earnings data. Why it matters Earnings drift is a market inefficiency. If prices drift predictably, traders can profit by buying after positive surprises and holding. Research shows that earnings drift is substantial: prices drift for 2-8 weeks after earnings. Mechanism Why does earnings drift persist? Theories include: - Underreaction: market doesn't fully process the earnings surprise initially - Slow information diffusion: not everyone immediately understands implications - Anchoring: market anchors on prior forecasts and adjusts gradually Practical example A stock is expected to earn 1 dollar per share. It actually earns 1.20 dollars (20 percent beat). The stock jumps 8 percent on the announcement. A fair valuation increase for a 20 percent earnings beat might be 15-20 percent. So there is still 7-12 percent of drift. Over the next 4 weeks, the stock drifts upward another 10 percent as the market fully reprices the higher earnings. Profitability Earnings drift trading is popular with quantitative funds. Buy after earnings beats, hold for 2-4 weeks, expect outperformance. See also - Post-Announcement Drift - Earnings Surprise - Underreaction - Momentum Trading
