I measured the stock move on the first trading session after every quarterly earnings release by current S&P 500 companies since April 2020: 12,353 reports from 493 companies. The average move was 4.6% and the median 3.3%, about three times a normal day for the same stock. The part I didn't expect is how much bigger the moves have become.
| Reports from | Reports | Average move | Median move | Moved 10% or more |
|---|---|---|---|---|
| Apr to Dec 2020 | 1,361 | 4.0% | 3.0% | 6.3% |
| 2021 | 1,852 | 3.4% | 2.6% | 4.4% |
| 2022 | 1,870 | 4.6% | 3.3% | 8.8% |
| 2023 | 1,883 | 4.4% | 3.3% | 8.7% |
| 2024 | 1,920 | 5.1% | 3.9% | 12.6% |
| 2025 | 1,916 | 5.0% | 3.6% | 12.3% |
| Jan 1 to Oct 23, 2026 | 1,551 | 5.3% | 3.9% | 13.3% |
In 2021 about one report in 23 moved the stock 10% or more. This year it's more than one in eight.
Five findings
1. It isn't index turnover. Newer, more volatile companies joining the S&P 500 could explain the trend, so I reran it on the 358 companies that reported in every year. Their average move went from 3.3% in 2021 to 5.2% in 2026, and the 10% share from 4.1% to 13.2%. Same picture.
2. After the close moves more than before the open. Releases after the close were followed by a 5.1% average move, against 4.1% before the open. Part of that is who reports when: technology companies put out 68.5% of their results after the close, industrial companies 22.7%. The after-close share itself has stayed between 43% and 45% a year.
3. Sector matters more than anything else. Over the last four quarters, technology stocks moved 8.0% on average and 28.2% of their reports moved the stock 10% or more. Utilities moved 1.9%. Eight of the ten calmest stocks on earnings are utilities.
4. The big moves don't keep going. Of the 4,119 reports followed by a move of 5% or more, the stock moved further in the same direction the next day 51.4% of the time, and the average next-day follow-through was 0.06%. A coin toss.
5. This October has been calm, so far. The 108 reports from October 1 to 23 moved stocks 3.6% on average, against 4.0% in the same weeks of 2025. The early weeks are mostly banks and industrial companies, though, and next week 133 S&P 500 companies report. Microsoft has averaged 7.0% over its last eight reports, Intel 9.3%, Eli Lilly 8.4% and Alphabet 4.1%; Twilio (15.8%) and Reddit (14.7%) are among the biggest movers on the list.
How I measured it, and the traps
- The release time comes from the SEC. Each release is the company's item 2.02 8-K, timed by its EDGAR acceptance timestamp. Before 4 p.m. New York time, I use that day's close-to-close return; after the close, the next session's.
- Don't trust one timestamp field. The
acceptanceDateTimein EDGAR's submissions JSON didn't always agree with the acceptance time in the filing's own header file (.hdr.sgml), sometimes by several hours, which is enough to move a release across the close. Where the two disagreed about the trading day, I used the header. - Pick the right 8-K. Some companies file a preliminary 2.02 8-K days before the real results. My first rule grouped 2.02 filings within ten days of each other, which merged those pre-announcements with the real release. Keeping the latest one on or before the call date fixed it.
- Check against something you know. For calls with a known start time, the inferred reaction day agreed with the call time 98.4% of the time.
- Watch for rules that create trends. An early version treated a morning call as proof of a before-open release. It produced a neat finding that after-close releases were rising. They weren't; the rule was. Without it the share is flat.
- Splits and the market. I excluded windows around stock splits, compared each move with the stock's median daily move over the previous 55 sessions, and checked a market-adjusted version: subtracting the median S&P 500 move that day only lowers the average from 4.6% to 4.5%.
Check a stock before it reports
With the Equibles MCP server connected to Claude or ChatGPT, a prompt like "Using Equibles, how much did Microsoft's stock move the day after each of its last eight earnings reports?" pulls the call dates and the daily prices and does the arithmetic.
The full study has the quarterly series, the sector table, the stocks that move most and least, the twelve biggest single moves since 2020 (AppLovin's +46.3% on November 7, 2024 leads) and next week's reporters with the biggest past moves: How Much Do Stocks Move After Earnings? Evidence From 12,353 S&P 500 Reports.
