Key Highlights

  • Commentary on Wednesday, October 28, 2026 restated that November through April has historically outperformed May through October, and no statistics accompany it, so any use of the idea requires independent measurement over defined windows.
  • A sound test fixes the windows, the index and the return measure in advance, compares the two halves in every year and reports the spread with its range and not a single average.
  • Confirmation would need a stable spread across subperiods and indices, while refutation would follow if the spread vanishes after small changes to the start date or if a few outlier years explain it.
  • Closing levels of Tuesday, October 27, 2026 for the Nasdaq Composite at 26,477.81 and the S&P 500 at 7,722.60 can serve as reference points for the window that begins on Monday, November 2, 2026.

Setting Up a Fair Comparison

A fair test starts with definitions. The windows are November through April and May through October, the index is chosen before results are viewed, and returns are measured the same way in each half, including whether dividends are counted. Each calendar year then yields one pair of results, so the unit of analysis is the year and not the month. The spread between the two halves is recorded for every year, and the full distribution is reported, including the years in which the pattern failed. For the current cycle, the Nasdaq Composite closed at 26,477.81 and the S&P 500 at 7,722.60 on Tuesday, October 27, 2026, which can serve as reference levels for the window beginning on Monday, November 2, 2026. The material available holds no historical figures, so none are supplied here.

How Robustness Checks Separate Pattern From Chance

Robustness checks are the core of the exercise. The start date can be shifted by a month in either direction to see whether the spread survives. The sample can be split into early and late subperiods to test stability, and a different index can be used to test breadth. Outlier years can be removed to see whether a few episodes explain the result. A shuffled version of the data, with months assigned at random, shows how large a spread chance alone can produce. The rate environment also deserves a control, since a period of rising rates differs from one of falling rates. A pattern that passes these checks earns a modest weight, while one that fails them is better treated as description.

Risks and What to Watch

The bull reading is that a spread which persists across indices, subperiods and start dates offers a small, repeatable edge. The bear reading is that most calendar rules weaken once costs, taxes and crowding are counted. Three risks apply. Data mining risk arises when many windows are tried and only the best is reported. Look-ahead risk arises if the window was chosen with knowledge of the outcome. Regime risk arises if a new rate setting breaks old relationships. Investors should watch the Fed decision at 2:00 p.m. ET on Wednesday, October 28, 2026, the results from Microsoft (NASDAQ:MSFT) and Alphabet (NASDAQ:GOOGL) after the close and the first window session on Monday, November 2, 2026, with the window ending in April 2027.

Where Things Stand

The answer is that investors can test the Halloween indicator by fixing the windows and index in advance, comparing the two halves in every year and checking whether the spread survives shifted start dates, subperiods and outlier removal. The material available contains no historical figures, so the pattern remains untested here. The reference points are the Nasdaq Composite at 26,477.81 and the S&P 500 at 7,722.60 on Tuesday, October 27, 2026. The next catalysts are the Fed decision on Wednesday, October 28, 2026, the technology results after the close and the window start on Monday, November 2, 2026, and this is not investment advice.