Altcoin Season Index: Methodology and How to Trade It
"Altseason" is crypto Twitter's most overused word — and at the same time a real, measurable market state. The Altcoin Season Index turns the feeling that "alts are flying" into a single number from 0 to 100. Here's exactly how we calculate it, where the metric's limits are, and how to read it without fooling yourself.
The formula: what gets counted and how
The index answers one question: what share of large altcoins outperformed BTC over the last 90 days. Take the top 50 coins, score each "coin vs BTC" pair, and the alts' share of wins is the index value. A reading of 80 means four out of five large alts beat BTC over the quarter; 20 means BTC outplays four out of five.
Three implementation details worth knowing. First: we select the top 50 by futures open interest rather than market cap — OI better reflects what's actually being traded and automatically filters out dead coins with inflated caps. Second: stablecoins and wrapped tokens (WBTC, stETH and the like) are excluded — their "returns" say nothing about rotation. Third: everything is computed on our own price data, no third-party APIs.
Zone thresholds: 75 and above — altcoin season; 55–74 — alt bias; 45–54 — neutral; 25–44 — BTC bias; below 25 — Bitcoin season.
Rotation mechanics: why the index moves in cycles
Capital in crypto climbs a familiar ladder: money enters BTC first (low index, rising dominance), then profits rotate into ETH and large alts (the index crawls toward the middle), and finally into small caps and memes (the index above 75, euphoria). The Altcoin Season Index is the market's position on that ladder — measured, not felt.
That's its practical meaning: it doesn't predict where the market goes next, it tells you which phase of the rotation you're in. High readings have historically coincided with the late, euphoric stage of bull cycles — followed by cooling. Persistently low readings mark fear and accumulation phases, when all the risk appetite fits inside BTC.
How to use it — and how not to
As an allocation compass. The index is useful for slow decisions: in a BTC season, a basket of ten alts statistically loses to simply holding BTC; the index turning up from low readings is the moment to revisit proportions. It's a tool of weeks and months, not days.
Not as an entry timer. The index is built on a 90-day window — inert by construction. By the time it crosses 75 and "altseason is confirmed", much of the move is behind you. For timing you need fast metrics: alts' open interest, funding, volumes.
Cross-check with dominance. The index and BTC dominance look at the same phenomenon from different angles and should agree: the index rises while dominance falls. A high index with dominance not falling is a dirty signal — most likely a narrow group of coins spiked, not the market.
FAQ
Why a 90-day window?
A quarter is the compromise: a short window (a week or a month) turns the index into a noisy oscillator where every memecoin pump moves the reading; a long one (six months or a year) makes it uselessly inert. 90 days is enough to capture a regime change and short enough to notice it while the trend is alive. It's also the window used by the widely accepted methodology of this index.
The index reads 90 — time to load up on alts?
More likely the opposite: extreme readings mean the rotation into alts has already happened and the market is in its late, euphoric phase. Historically that's the zone for reducing alt risk, not adding it. Buying alts "because altseason is confirmed" is buying someone else's profit.
Where can I check the index?
The live value with a per-coin breakdown is on the Altcoin Season Index page. Next to it: BTC dominance for cross-checking and the Fear and Greed Index for market temperature.
Altcoin Season Index · BTC Dominance · Open Interest · Fear and Greed