History says Bitcoin has a narrow line in September, and slipping below it has always meant a red month — a warning sign for buyers hoping for a strong autumn.

• Over 15 years, every September that dropped more than 11% below its opening price finished in the red.
• The deepest dip that still recovered was 2024, which fell almost 11% and still closed up 7.5%.
• The shallowest losing September, 2022, fell 9.5% — leaving a thin gray zone between roughly 9.5% and 11%.
• Above that band, a dip is normal. Below it, no September has ever clawed its way back to a green close.
• New monthly lows after the first week of September would be the clearest bad signal.

Outlook: Bitcoin's direction in early September will likely set the tone for the whole month, and a break below that band would point to a losing month.