A simple timing pattern in Bitcoin's monthly price history has been right almost 9 times out of 10, and it gives traders an early read on whether a month will close up or down — useful, though not a guarantee.

• The rule is basic: if the month's low comes before its high, the month usually closes green; if the high comes first, it usually closes red.
• Across all 179 complete months of Bitcoin's history, that first extreme picked the right direction 89% of the time.
• Green months follow the pattern 93% of the time; red months 84% of the time.
• In September specifically it has worked 14 out of 15 years, with 2015 the lone miss — it topped first, traded weak all month, then squeaked out a small gain.
• This is not just a September quirk; the same signal holds across every other month too.

Outlook: Whichever extreme Bitcoin sets first in September will be the early tell for how the month finishes.