The Altcoin Season Index measures breadth: how many altcoins have outperformed Bitcoin over a set period. It answers the rotation question with a single reading, rather than with whichever handful of coins someone happens to hold.

There is no single universal index. CoinMarketCap uses the top 100 eligible coins over 90 days, while BlockchainCenter uses the top 50. Both exclude stablecoins and asset-backed tokens, and both call it altcoin season when 75% of the sample has beaten Bitcoin.

How the index is calculated

Each eligible coin is compared with Bitcoin over the lookback period, commonly 90 days. The score is the share of the sample that beat Bitcoin, scaled from 0 to 100.

Each coin gets one vote, so the index captures how widespread outperformance is rather than how large it is. That is the key difference from Bitcoin Dominance, which is weighted by market cap.

A season is a condition, not a day

A season means outperformance that has persisted, not a single week that went one way. These states have historically lasted months, so week-to-week swings around the trend are ordinary noise rather than turning points.

The lookback period decides what counts as a season in the first place. A shorter period flips far more often and describes something closer to this month, which is a different question.

Underperforming and falling are different claims

A reading that favours Bitcoin is often heard as altcoins going down. It only says they are gaining less, which is compatible with them gaining a great deal. Equally, altcoins can outperform Bitcoin in a falling market simply by falling less. Read the index alongside absolute returns and the direction of the total market.

What it does not tell you

It does not measure quality, liquidity or whether a coin is investable. A token counts once if it is eligible, regardless of those differences.

It says nothing about why capital is moving. Rotation can be driven by policy, narrative or plain fashion, and none of that shows in the score.

The sample changes as rankings change, so historical readings compare an evolving basket rather than a fixed one. A season can also be under way in one corner of the market and absent from the rest, which a single number cannot show.

How to read it

Altcoin season. Most of the field is beating Bitcoin, and money is moving outward into the rest of the market.

Neutral. No decisive rotation in either direction.

Bitcoin season. Few altcoins are keeping up, and capital is concentrating into Bitcoin.

The Altcoin Season Index is one of the views on the Relative Performance dashboard, alongside BTC Dominance, Altcoin Breadth and BTC vs Field.

Related metrics: Bitcoin Dominance (BTC.D), Altcoin Breadth and Advance / Decline.

Common questions

What is the altcoin season threshold?

On both CoinMarketCap’s and BlockchainCenter’s versions, it is altcoin season when 75% of the sample has outperformed Bitcoin over 90 days. A reading of 25 or below is usually labelled Bitcoin season.

How is this different from Bitcoin Dominance?

Dominance is weighted by market cap, so a few large coins decide it. The Altcoin Season Index gives each eligible coin one vote, which makes it a breadth measure.

Does a high score mean altcoins rose?

No. They only need to outperform Bitcoin. In a falling market, that can mean losing less.

Why 90 days?

It is a common convention, not a rule. Shorter windows flip more often and describe something closer to a monthly move than a season.

Why do providers disagree?

They use different sample sizes, exclusions, data cut-offs and thresholds. Name the source before comparing two scores.