Berkshire Hathaway A Slumps 1.1% as $340M Volume Surges to 371st in U.S. Trading Activity

Berkshire Hathaway A (BRK.A) closed on October 1, 2025, with a 1.10% decline, marking its lowest intraday level since mid-September. The stock traded with a volume of $340 million, a 33.23% increase from the previous trading day, ranking 371st in trading activity among U.S. equities. Market participants noted the move followed a consolidation phase after a six-day rally in late September, though no major earnings or strategic announcements were reported by the conglomerate during the period.

Analysts highlighted that the selloff occurred amid broader market uncertainty over global growth outlooks, with investors rotating into defensive sectors. While Berkshire’s insurance underwriting results for the quarter were in line with estimates, the lack of new major acquisitions or regulatory developments limited near-term catalysts. The decline also reflected technical selling pressure as the stock approached key Fibonacci retracement levels identified by quantitative traders.

To run this back-test robustly I need to pin down a few practical details that aren’t fully specified yet:

1. Stock universe • Should we limit ourselves to all U.S.-listed common stocks (NYSE + NASDAQ), or do you want a different universe?

2. Portfolio construction • Equal-weight each of the 500 names every day (default), or use another weighting (e.g., volume-weighted)?

3. Trade execution price • Enter positions at the next day’s open and exit at the same day’s close (1-day holding period), or enter/exit using close-to-close prices (buy at today’s close, sell at tomorrow’s close)? (I will default to “buy at today’s close, sell at tomorrow’s close” if you don’t have a preference.)

4. Frictional costs • Should we assume zero trading costs, or would you like to include a per-trade commission or slippage estimate?

Let me know your preferences (or confirm the defaults above) and I’ll set up the data retrieval plan and run the back-test.