Buying and selling a stock on the same day is completely legal and forms the fundamental basis of day trading, swing trading, and routine intraday market liquidity. Millions of retail investors, professional day traders, and institutional market makers execute same-day transactions regularly across global stock exchanges. The only context where same-day trading becomes illegal is if it involves illegal market manipulation practices, such as pump-and-dump schemes, insider trading based on material non-public information, or unlawful spoofing designed to artificially distort public market prices.