According to @StockMKTNewz, the S&P 500’s biggest up day in 2025 was April 9 at +9.5%, followed by May 12 +3.3% and April 22 +2.5%, with the remaining top sessions on March 14 +2.1%, May 27 +2.0%, April 24 +2.0%, January 15 +1.8%, April 11 +1.8%, March 24 +1.8%, and April 23 +1.7% (source: @StockMKTNewz on X, Dec 28, 2025). Seven of the top ten sessions occurred in April–May 2025, offering clear calendar anchors for momentum and mean-reversion backtests in SPX futures and sector ETFs using this date set (source: @StockMKTNewz on X, Dec 28, 2025). Crypto traders can map BTC and ETH performance on these same dates to evaluate cross-asset risk behavior using the provided list (source: @StockMKTNewz on X, Dec 28, 2025).