Altcoin Season Index Explained: When Do Alts Actually Outperform Bitcoin?

How it's calculated

Alphabit's Altcoin Season Indexstarts from the top 50 coins by market cap, strips out stablecoins, wrapped/staked duplicates, and tokenized treasuries — none of those are altcoin bets in the sense the index is trying to measure — then computes each remaining coin's trailing 90-day return against Bitcoin's over the same window. The index itself is simply the percentage of that set that beat Bitcoin.

A handful of top-50 coins get skipped in any given run — ones without a matching listing on the price source used, or without enough trading history yet — and the index is computed over whatever set remains scoreable, disclosed on the page itself rather than silently ignored.

How it's historically been read

A reading of 75 or above — three-quarters of the top 50 beating Bitcoin over three months — has conventionally been called altcoin season: capital broadly rotating out of Bitcoin and into smaller-cap alternatives chasing higher beta, typically a later-cycle, higher-risk-appetite phase.

A reading of 25 or below is Bitcoin season— capital concentrating in Bitcoin specifically, which has historically shown up both early in a bull cycle (Bitcoin leads, alts lag) and during risk-off periods (Bitcoin is treated as the relatively safer crypto asset in a drawdown). The same reading can mean two different things depending on the broader trend, which is why it's read alongside price direction, not in isolation.

Limitations

The 75/25 thresholds are a convention borrowed from common industry usage, not a statistically derived boundary — treat a reading of 72 and a reading of 78 as more similar than the "no clear season" vs. "altcoin season" labels might suggest. The index is also a snapshot of the specific 50 coins large enough to qualify today; survivorship and reshuffling in and out of the top 50 over time mean long-run historical comparisons should be read with some caution. It's context for allocation, not a timing signal — see Bitcoin Dominance for the closely related market-cap-share view of the same rotation.