Bitcoin traders are heading into a month with a bad reputation, but the early days should show quickly whether this September turns out good or bad.

• September has closed lower for Bitcoin in nine of the last fifteen years.
• In every one of those losing Septembers, the month's high came before its low — the drop came later.
• Every September that put in its low in the first few days finished higher.
• That makes the first four days the tell: an early dip is the bullish setup, an early rally is the warning.

Outlook: If Bitcoin bottoms in the opening days of the month, history points to a green September; a strong start instead suggests the high is already in.