Altcoin Season Index
Is the rally broad or is Bitcoin carrying the whole market? This gauge counts how many of the top 50 coins have beaten BTC over the past 30 days — the cleanest single measure of altcoin breadth.
—calculating…
Strongest vs BTC (30d)
- Loading…
Why breadth beats headlines
Every cycle produces the same argument: someone’s favorite altcoin doubles and Twitter declares altseason. Breadth cuts through anecdotes. If only five of the top fifty coins beat Bitcoin, those doubles are stock-picking luck inside a Bitcoin-led market. When forty of fifty beat it, holding BTC is what costs you money. The index simply counts which world you are in.
Historically, deep altseasons — readings sustained above 75 — arrived months after a Bitcoin top in dominance terms, as profits rotated down the risk curve from BTC to large caps to small caps. The 2021 cycle ran that script twice. Watching this gauge alongside BTC.D lets you see the rotation while it happens instead of reading about it afterward.
Frequently asked questions
What counts as an altcoin season?
The common convention: when at least 75% of the top 50 coins (stablecoins and wrapped assets excluded) outperform Bitcoin over the measurement window, the market is in altcoin season. Below 25%, Bitcoin season. Everything between is rotation territory without a clear winner.
Why does this page use a 30-day window?
The classic index measures 90 days; our live widget uses the 30-day return that market APIs expose in a single request, which reacts faster to regime changes. The trade-off is more noise — treat a fresh flip as provisional until it persists for a week or two.
How does the index relate to Bitcoin dominance?
They are mirror images measured differently. Dominance weighs capital: it moves when big caps move. This index counts breadth: every coin votes equally, so it catches broad altcoin rallies that a few mega-caps can mask in the dominance number.
Should I buy altcoins when the index is high?
A high reading confirms a trend that is already running — by the time 80% of the top 50 beats BTC, much of the move has happened. Practitioners more often use extreme lows as accumulation signals and extreme highs as a cue to tighten risk. This is information, not investment advice.