Bitcoin Faces a September Standoff: Big Investors Depart as Whales Continue to Amass

Bitcoin Faces Heightened Selling as On-Chain Data and Seasonal Patterns Point to Capital Outflows, While Altcoins Capture 61% Market Share

Bitcoin is encountering growing selling pressure in September 2025, as on-chain indicators and previous market patterns reinforce worries about ongoing capital exits. Both the Selfish Mining Index (SOPR) and the Sharpe Ratio suggest negative net movement, hinting at investors shifting towards realizing gains and reducing exposure to risk. At the same time, altcoin market share has reached 61%, indicating capital may be moving away from Bitcoin to other digital assets. These shifts coincide with Bitcoin’s typical September weakness, with the price now trading near $110,383—a drop of 11.6% from its August high of $124,533.

The so-called "September Effect," a recurring downward trend that has appeared in eight of the past twelve Septembers, averages a 3.77% monthly decrease since 2013. This trend is often attributed to institutional portfolio adjustments, tax-related selling, and a seasonal reduction in risk appetite. Current technical analysis highlights Bitcoin’s fragility, with its price falling below a key support level at $110,500, and new crucial thresholds at $108,000 and $107,400. If Bitcoin dips below $100,000—a major psychological barrier—further declines may occur, though some experts believe this area could become a short-term buying opportunity.

Mining activity has added to recent weakness, with August seeing an unprecedented surge in Bitcoin transferred from miners to exchanges. According to CryptoQuant, Bitcoin’s Miner Reserve—the amount held by miners—hit a high in July before decreasing as miners sold off assets to secure profits amid rising operational costs. This selloff led to an 8.7% outflow in August, further amplifying seasonal pressures. Institutional investors, meanwhile, have exhibited mixed behavior: while the number of large holders (whales) has hit a record 19,130 addresses,

ETFs have experienced $751 million in outflows, reflecting a push and pull between those with long-term convictions and short-term sellers.

Weakness in the U.S. dollar and potential Federal Reserve interest rate cuts could provide future support for Bitcoin. The DXY, which measures the dollar’s value, has declined by 10% this year, and Bitcoin’s negative correlation with the dollar has lessened to -0.25, the lowest in two years. Market watchers believe that a shift in Fed policy may boost liquidity for riskier assets, positioning Bitcoin and altcoins to gain. Nonetheless, caution prevails, as recent volatility—including a $1.7 billion liquidation in early September—highlights the instability of current prices.

Even with bearish signals, some analysts point to similarities with Bitcoin’s recovery in September 2017, where a consolidation period was followed by a strong upward move. Positive technical patterns, such as a bullish divergence in the RSI and a stabilizing range between $107,000 and $110,000, indicate the possibility of a rally toward $120,000. However, this outcome depends on continued dovishness from the Fed and persistent accumulation by large investors. The high level of altcoin dominance at 61% also adds complexity, as investors shift into smaller assets while Bitcoin consolidates.

The weeks ahead will challenge Bitcoin’s ability to withstand mixed signals. While seasonal trends and on-chain outflows remain, broader economic factors like dollar weakness and possible rate cuts could spark a reversal. Traders are set to closely follow the PCE inflation report on September 26 and remarks from Federal Reserve Chair Jerome Powell for guidance on monetary policy. For now, the $100,000 level stands as a pivotal support; a drop below this could deepen the downward momentum.