September has long carried a bad reputation in crypto. Both Bitcoin and Ethereum have repeatedly stumbled during this month, with history showing sharp pullbacks or muted performance. It is widely considered the weakest month for crypto, but 2025 looks different in several ways: both assets have recently touched new all-time highs, ETF flows now shape market liquidity, and rate cuts are back on the table.
The question is whether September’s weakness will once again weigh on crypto, or whether this cycle has shifted. And whether these two crypto stalwarts — Bitcoin and Ethereum — will again move together, either in thick or thin. Or will there be a change of fate for one of them?
Exchange Reserves and Withdrawals Tell a Mixed Story
Bitcoin’s exchange reserves dropped about 18.3% from last September, while Ethereum’s reserves fell roughly 10.3%. This looks interesting, considering both assets are currently trading quite close to their all-time highs.
Both point to long-term accumulation trends, as fewer coins sit on exchanges ready to sell.
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But withdrawing addresses paints a more complex picture.
Ethereum’s withdrawing addresses climbed from 53,333 in 2024 to more than 60,000 this year, reinforcing the bullish case of stronger self-custody and accumulation.
Bitcoin, on the other hand, saw withdrawing addresses fall sharply from 35,347 last year to just 11,967 at press time, showing a weaker preference for self-custody and potentially softer accumulation demand, yet. But there is more to this picture.
Even though Bitcoin’s accumulation demand looks weak on paper, it leaves room for price growth if a positive driver like the September 2025 rate cuts arrives. With Bitcoin’s history of stronger ETF inflows in September compared to Ethereum, the low number of withdrawing addresses could be less a sign of weakness and more a setup for incoming demand.
Profit Supply and the Risk of Selling Pressure Looms On Both
Both Bitcoin and Ethereum now show a much higher percentage of supply in profit than a year ago. For Bitcoin, the share rose from 76.91% in September 2024 to 88.17% in September 2025. Ethereum’s percentage jumped even higher, from 73.83% to 92.77%.
This means most holders are sitting on gains, historically a setup that encourages profit-taking.
With both assets near record highs during what is usually the weakest month for crypto, September could see increased selling pressure — unless offset by structural inflows elsewhere. And just looking at pure numbers, ETH remains a high-risk case.
ETFs Add a New Dimension in 2025
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This year introduces a variable that past Septembers did not have at this scale: ETF flows. Since launch, Bitcoin ETFs have drawn around $54.5 billion in lifetime inflows, while Ethereum ETFs — the newer product — have pulled in about $13.3 billion.
In the last 30 days, Ethereum ETFs saw net inflows of $4.08 billion, compared with outflows of $920 million for Bitcoin ETFs. That contrast has led many to say ETH is winning in this cycle.
But digging into September data shows a different story. For September 2025 so far, Ethereum ETFs are already in the red with almost $135 million in net outflows.
This repeats a similar trend from last September, which was also negative. Bitcoin, by contrast, started this September with $332 million in net inflows, similar to September 2024, when BTC ETFs logged $1.26 billion in gains.
That pattern suggests September and rate cuts have consistently favored BTC over ETH when it comes to ETF flows. Even with ETH’s big summer inflows, its track record in September shows weakness.
As Jeff Dorman put it:
“BTC is gold, but very few care about gold. ETH is an app store — and tech investing is a bigger market, he said on X”
That helps explain why ETH has pulled growth capital. Still, in the weakest month for crypto, structural flows continue to tilt toward Bitcoin. This possibility is what we discussed earlier in the ‘Withdrawing Activity’ section.
ETH/BTC Ratio and Market Dominance Point To Strength In Bitcoin
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The ETH/BTC ratio has slipped from 0.043 last September to 0.038 today.
That decline shows Ethereum underperforming relative to Bitcoin despite ETF momentum, year-on-year.
Meanwhile, Bitcoin’s dominance rose from 57.46% to 58.82% over the same period, while Ethereum’s dominance fell from 15.02% to 13.79%.
In other words, even with Ethereum showing better near-term ETF flows, Bitcoin continues to hold structural leadership.
This reinforces why markets still treat BTC as the risk benchmark, particularly in the weakest month for crypto.
Short Squeeze Potential Tilts Toward Bitcoin
Another short-term element is liquidation data. In the 30-day timeframe, Bitcoin has $5.24 billion in short positions stacked against just $1.83 billion in longs. This imbalance increases the chance of a short squeeze if prices move higher.
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Ethereum looks more balanced, with $6.55 billion in shorts and $6.10 billion in longs.
That tilt suggests that if September produces any surprise upside during what is usually the weakest month for crypto, Bitcoin is better positioned to rally sharply on forced liquidations.
The X Community also believes derivatives to hold the key in September:
Analysts Still Warn of Choppiness
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Despite these setups, forecasts from analysts remain cautious. For Bitcoin, they warn that failure to hold $107,557 support could open a deeper correction toward $103,931, even as upside remains possible if resistance near $111,961 breaks.
For Ethereum, the picture is similarly uncertain. Analysts point to resistance around $4,579 and downside risks if the price closes below $4,156. Choppy range-bound movement remains the base case, reinforced by high profit supply and divergence on RSI signals. Simply put, selling pressure would still outweigh the rallying attempts if the usual September narrative holds.
September’s Outlook: Weakest Month for Crypto, But Context Has Changed
September has often been the weakest month for crypto, with BTC and ETH both showing poor track records. The rare gains in 2023 and 2024 did little to shift that trend.
In 2025, the setup looks different: both coins are near record highs, ETFs are driving flows, and another rate cut is expected. The last September rate cut — a 50 bps move in 2024 — aligned with stronger Bitcoin flows (remember ETFs), not Ethereum.
This time, high profit supply and weak self-custody still point to selling. Both BTC and ETH may face headwinds, but if there is upside, Bitcoin is more likely to lead with the accumulation demand supposedly increasing. Altcoins linked to Ethereum may not benefit, leaving the wider market under pressure.
Source: https://beincrypto.com/bitcoin-vs-ethereum-september-2025/