The Altcoin Season Index reduces a complicated question — is capital rotating out of Bitcoin into everything else? — to a single number between 0 and 100. It is a genuinely useful summary and a genuinely misleading one, depending entirely on whether you know what is inside it.
This article is for informational and educational purposes only. It is not financial advice, investment advice, or a recommendation to buy, sell, or hold any security, cryptocurrency, or financial product. Always verify data with official sources before making financial decisions.
Short answer: how the index is built
Short answer: The index counts how many of the top 50 cryptocurrencies by market capitalisation have outperformed Bitcoin over the trailing 90 days, then expresses that count as a score out of 100. If 75% or more have beaten Bitcoin, the index declares “altcoin season.” If 25% or fewer have, it declares “Bitcoin season.” Everything between is neither.
| Component | Specification |
|---|---|
| Universe | Top 50 coins by market cap |
| Typical exclusions | Stablecoins and wrapped/pegged assets |
| Lookback window | 90 days |
| Benchmark | Bitcoin |
| Altcoin season threshold | 75% or more outperforming |
| Bitcoin season threshold | 25% or fewer outperforming |
The 75% rule and the 90-day window
Both parameters are arbitrary, and both do real work.
The 75% threshold is a convention, not a statistically derived level. Nothing distinguishes 74% from 76% except which label appears on the dial. Treating the crossing of that line as an event is a category error — the underlying variable is continuous and the label is a bucket someone chose.
The 90-day window matters more. It is long enough that a single sharp week does not flip the reading, and short enough that the index can move meaningfully within a quarter. But it also means the index is describing something that already happened over three months. It is a rear-view measure of completed relative performance, not a forward signal, and the lag is structural rather than incidental.
Bitcoin dominance is not the same signal
These two metrics get used interchangeably and measure different things.
Bitcoin dominance is Bitcoin’s share of total crypto market capitalisation — a value-weighted measure. The Altcoin Season Index counts coins — an equal-weighted measure. A month in which two megacap altcoins surge and forty-five small ones fall will push dominance down while the index stays firmly in Bitcoin-season territory. The reverse also happens: broad small-cap strength with flat majors lifts the index while leaving dominance unchanged.
Reading them together is more informative than reading either alone. Dominance falling while the index stays low means concentration in a few large alternatives. Both moving together means genuine breadth.
Survivorship: the top-50 list rewrites itself every cycle
This is the index’s most serious methodological weakness and it is almost never mentioned.
The universe is defined as the current top 50 by market capitalisation. Coins that collapsed out of the top 50 are not in it. Coins that recently entered — often because they just ran hard — are. The measurement therefore systematically includes recent winners and excludes recent losers, which biases the outperformance count upward during periods when new entrants are climbing the table.
The composition turnover is substantial. Comparing an index reading from one cycle to a reading from another is comparing two different baskets that share a name and a methodology but not their contents. Historical charts of the index across multiple years imply a continuity that does not exist.
Why stablecoins and wrapped assets distort the count
Most implementations exclude stablecoins, and they should — a dollar-pegged token will underperform Bitcoin in any rising market and outperform in any falling one, purely mechanically, which would make the index a noisy inverse Bitcoin indicator.
Wrapped and staked derivatives are the subtler problem. Assets that track Bitcoin or Ethereum one-for-one are not independent observations; including them double-counts an underlying asset and dilutes the breadth the index claims to measure. Implementations differ in how aggressively they filter these, which is why two sites can publish different values for the same day. If a reading matters, check the provider’s exclusion list rather than assuming a standard.
Reading the index alongside funding rates and ETH/BTC
The index is most useful as one input among several, because it says what happened without saying what is driving it.
The ETH/BTC ratio is the single most common companion, since Ethereum has historically led broader alternative-asset strength; the index rising while ETH/BTC falls suggests strength concentrated away from the largest alternatives. Perpetual futures funding rates add a positioning dimension — an index climbing on persistently elevated funding describes a leveraged move with a different risk profile than the same reading with neutral funding. Aggregate open interest and stablecoin supply growth round out the picture by showing whether new capital is entering or existing capital is rotating.
Mini glossary
- Altcoin. Any cryptocurrency other than Bitcoin. The definition is contested and some frameworks exclude Ethereum.
- Bitcoin dominance. Bitcoin’s market capitalisation as a share of total crypto market capitalisation.
- ETH/BTC ratio. Ethereum priced in Bitcoin. A common proxy for appetite for assets beyond Bitcoin.
- Funding rate. The periodic payment between long and short holders of a perpetual futures contract that keeps its price tethered to spot. Persistently positive funding indicates crowded long positioning.
- Survivorship bias. Distortion introduced by measuring only entities that remain in a sample, excluding those that failed out of it.
What this article does not conclude
The index is a description of trailing 90-day relative performance across a shifting basket of fifty assets. It is not a forecast, it does not identify rotation before it happens, and its thresholds are conventions rather than findings. Readings near the boundary carry no more information than readings in the middle.
Different providers publish different values using different exclusion rules. Where a specific figure matters, check the methodology page of the source you are quoting.