Bitcoin up 25 percent in August faces September test as 'Red September' jinx looms

Bitcoin has again come up against statistics showing it has closed lower in September 8 times over the past 13 years, making it the weakest month of the year.

On Sept. 1, blockchain media outlet Decrypt reported that bitcoin ended 8 of the 13 Septembers since 2013 in negative territory. Its average return was minus 2.97 percent and the median was minus 2.44 percent.

So-called "Red September" is a September weakness pattern repeatedly cited in the crypto market. It means the typical September trend itself was weak rather than a few sharp drops dragging down the average. Over the same period, the average return in June was minus 1.59 percent, while October was the strongest with an average of 19.92 percent and a median of 14.71 percent.

Looking at bitcoin's monthly performance, September weakness stands out more. Over the same period, October was tallied as the strongest month with an average of 19.92 percent and a median of 14.71 percent. That is the background for the term "Uptober" in the market.

Last year, however, this conventional wisdom was overturned. Bitcoin ended September 2025 up 5.16 percent, marking a third consecutive September gain, but October that followed ended lower for the first time since 2018.