Altcoin season, usually shortened to altseason, is a stretch of the market where most altcoins outperform Bitcoin at the same time. It is a relative measure rather than an absolute one. The Altcoin Season Index confirms one at a reading of 75 or above, meaning at least three quarters of tracked altcoins beat Bitcoin over the trailing 90 days.
Relative, not absolute
That distinction does more work than any other point on this page.
Rising 15% while Bitcoin rose 30% means an altcoin is losing badly. Beating Bitcoin is what altseason describes, rather than altcoins simply going up.
Traders track it because it shows where capital flows inside crypto, rather than whether crypto as a whole is rising.
How the index works
From Blockchaincenter comes the most cited version, measuring what share of the top 50 coins by market cap outperformed Bitcoin over the previous 90 days. Using the top 100, CoinMarketCap runs a separate one.
Both exclude stablecoins and wrapped tokens, since a stablecoin holding its peg says nothing about risk appetite.
| Reading | What it means |
|---|---|
| 75 and above | Altcoin season. At least three quarters of tracked altcoins beat Bitcoin over 90 days |
| 25 to 75 | Mixed market. Capital rotating without a clear leader |
| 25 and below | Bitcoin season. Bitcoin outperforming almost the entire field |
Note the 90-day lookback. By design, the index lags. It confirms that altseason happened and will not tell you one is about to start.
Bitcoin dominance, the other half
Bitcoin dominance, ticker BTC.D, is Bitcoin's market cap as a percentage of the total crypto market cap. Traders read it alongside the index because both describe the same rotation from different angles.
When dominance falls, money is leaving Bitcoin for everything else. When it rises, capital is concentrating in Bitcoin, usually defensively.
Wide is the historical range. During the 2021 altcoin run, dominance dropped to roughly 39%, meaning altcoins briefly held nearly two-thirds of the entire crypto market. On 18 June 2017, at the peak of flippening speculation, it fell to 40.6%. Through 2025 and into 2026 the pattern reversed, with dominance climbing back above 55%.
The rotation pattern
Altseason has historically followed a rough sequence, which is why traders watch for it in stages.
- Money enters Bitcoin first, frequently from outside crypto entirely.
- Bitcoin rallies, then stalls near a high.
- Profits rotate into Ethereum and the largest altcoins.
- Capital spreads down the market cap ladder into smaller tokens.
- Dominance falls, the index climbs, and altseason gets declared.
Descriptive, not a law. It held in 2017 and 2021. It has not repeated cleanly since, and there is a structural reason.
Why altseason keeps getting called early
Two things changed after 2021.
ETF flows run one direction. Spot Bitcoin ETFs gave institutional capital a regulated route into Bitcoin specifically, drawing $48.7 billion in 2024 and $47.2 billion in 2025. That money does not rotate down the risk curve. A pension allocator buying a regulated Bitcoin product is not selling it for a small-cap token three months later.
Token supply exploded. More than 20,000 assets now trade across major listing sites. The same rotating capital spread across ten times as many tokens produces a far weaker signal per token.
The result: dominance holding structurally higher than in previous cycles, with readings that would once have suggested rotation now sitting inside the mixed range.
What the index does not tell you
- It does not predict. A 90-day rolling window describes what already happened.
- It does not measure size. A reading of 76 means 76% of tracked coins beat Bitcoin, and says nothing about by how much.
- It does not distinguish quality. A token up 200% on a rumour counts identically to one up 200% on shipped product.
- It excludes most of the market. Top 50 or top 100 only, leaving smaller tokens invisible.
- The versions disagree. Blockchaincenter and CoinMarketCap can print different readings on the same day, because they track different sets.
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Frequently asked questions
What number confirms altcoin season?
A reading of 75 or above on the Altcoin Season Index, meaning at least 75% of tracked altcoins outperformed Bitcoin over the trailing 90 days. Below 25 is considered Bitcoin season.
How long does altseason last?
Historically weeks to a few months rather than years. The 2021 run stretched from roughly January to May, and sustained readings above 75 have been rare and short-lived across the index's history.
Does falling Bitcoin dominance always mean altseason?
No. Dominance can fall because Bitcoin is dropping faster than altcoins, which is a bear signal rather than a rotation. Dominance falling while total market cap rises is the combination that has historically preceded altseason.
Why do the different altcoin season indexes disagree?
They track different sets. Blockchaincenter uses the top 50 coins, CoinMarketCap the top 100. Both exclude stablecoins and wrapped tokens, and a wider set produces a different percentage on the same day.
Is altcoin season the same as a bull market?
No. A bull market means prices are broadly rising. Altseason means altcoins are rising faster than Bitcoin, which can happen inside a bull market, at the end of one, or during a sideways stretch.
Why has altseason not happened the way it used to?
ETF flows route institutional money into Bitcoin without rotating it onward, and the number of tradable tokens has passed 20,000, spreading the same rotating capital far thinner than in previous cycles.
What was the lowest Bitcoin dominance ever recorded?
Roughly 39% during the 2021 altcoin run, when altcoins as a group briefly held nearly two-thirds of the entire crypto market. Dominance also fell to 40.6% on 18 June 2017.
Can I predict altseason before it starts?
The index cannot, since it measures the previous 90 days. Traders watch dominance direction alongside total market cap for earlier signals, and neither has a reliable predictive record.
