Altcoin Season Index Plunges to 17 as Bitcoin Struggles - Crypto Economy

TL;DR

• The Altcoin Season Index fell to 17 as Bitcoin struggled, with altcoins 30% to 80% below all-time highs as 2025 winds down.
• The CoinMarketCap gauge compares the top 100 altcoins’ 90-day performance to BTC; readings below 20 show most are lagging, using a 1-100 score.
• Ethereum underperformed over 90 days, down 28.30% versus Bitcoin down 21.10%; an altcoin season needs 75+ and altcoins’ combined cap above Bitcoin.

A sharp reset in crypto sentiment is rippling through the altcoin complex as Bitcoin struggles to hold its ground. The report points to a profitability shift after Bitcoin fell from $126,000, and altcoins have borne the brunt, with major names down between 30% and 80% from their all-time highs. That drawdown has cooled calls for a classic altcoin season and pushed a key leadership gauge toward the floor. As 2025 winds down, the message is stark: for most tokens, relative performance is deteriorating, not improving. It remains among 2025’s lowest readings yet.

What the index captures

On CoinMarketCap, the Altcoin Season Index chart measures whether altcoins are outperforming Bitcoin over a 90-day window. It reviews the top 100 altcoins and compares their 90-day performance against BTC, then assigns a score from 1 to 100 based on how many of those assets are ahead. Put simply, the index tracks altcoins against Bitcoin to signal when market leadership has rotated away from the benchmark. When the score drops below 20, it suggests that losses, not catch-up rallies, are dominating the altcoin tape. The index has now fallen below 20 again.


At the time of writing, the index sat at 17, meaning only 17 of the top 100 altcoins have performed better than Bitcoin over the last 90 days. In the report’s framing, only 17 of the top 100 are beating Bitcoin, a configuration that points to an altcoin bear market. Ethereum, often treated as the bellwether for broader alt strength, is also lagging BTC: ETH posted a 28.30% decline over 90 days, while Bitcoin was down 21.10% over the same period. The reading implies most large caps are lagging, even as Bitcoin is down.

To qualify as an altcoin season under this framework, the index must read 75 or higher. That threshold is reached when the majority of altcoins outperform Bitcoin across a three-month stretch and their combined market capitalization surpasses the leading cryptocurrency. As a rule of thumb, 75 is the line that would signal an altcoin season, while readings closer to 100 can coincide with a market top. The last major altcoin season was in 2021, and the expected 2025 repeat has not arrived, with altcoin market cap trending low. Lower readings raise bear-market odds.