Bitcoin Defies Expectations with Surprise Gain in Historically Worst Month

Bitcoin's historically worst month has turned into a surprise gain of 7.8% so far in September, leaving investors wondering what this trend might mean for the fourth quarter.

A look back at past data from CoinGlass shows that Bitcoin lost value in eight out of 13 Septembers since 2013, with an average loss of about 2.9%. However, recent years have seen a shift away from this pattern.

In 2023, Bitcoin gained 3.9% in September, followed by 7.3% in September 2024 and 5.2% in September 2025. This year's positive trend is on track to become the fourth consecutive green September.

A green September typically leads to a strong fourth quarter for Bitcoin. In years where Bitcoin closed higher in September, including 2015, 2016, 2023, and 2024, the subsequent fourth quarters also saw gains of 57% in 2023 and 48% in 2024.

However, the pattern broke most recently in 2025, when a tariff threat from President Trump triggered about $19 billion in liquidations. To mirror the strong growth seen in 2023 or 2024, consistent buying from spot Bitcoin ETFs will need to occur throughout October.