There are at least five altcoin season indexes available for free. They disagree with each other constantly. And none of them tells you the thing that actually matters: whether the macro conditions supporting an altseason are sustainable.
The Thermometer Problem
The CoinMarketCap Altcoin Season Index measures the percentage of the top 100 coins (excluding stablecoins and wrapped tokens) outperforming Bitcoin on a rolling 90-day basis. A score of 75 or higher means altcoin season; 25 or lower means Bitcoin season. The Blockchain Center uses the top 50 coins with identical thresholds and found that the average altcoin season lasts approximately 18 days, with the longest historical streak reaching 117 days.
Source: Blockchain Center: https://www.blockchaincenter.net/altcoin-season-index/
CoinGlass offers a separate tracker. Glassnode uses an entirely different approach based on on-chain capital flow data — specifically, the positive second derivative of ETH Realized Cap and stablecoin supply.
Here is the problem: these indexes measure the symptom, not the cause. They tell you that altcoins are outperforming Bitcoin right now, which is roughly as useful as a thermometer telling you it’s hot outside. The question that matters is whether the conditions producing that heat are stable or about to reverse.
When Altseasons Fail
Altcoin rallies require supportive macro liquidity and collapse when conditions tighten. The evidence is unambiguous. During the 2022 crypto winter, the Fed began quantitative tightening, and while BTC fell 77% from $69,000 to $15,500, altcoins suffered even more — many experienced drawdowns exceeding 90%. In Q1 2026, TOTAL3 contracted by approximately $450 billion as elevated rates and a strong dollar drove institutional de-risking.
Source: Coinbase Institutional: https://www.coinbase.com/institutional/research-insights/research/monthly-outlook/monthly-outlook-apr-2025
Coinbase Institutional documented that the total crypto market cap excluding BTC fell 41% from its December 2024 high, attributing the damage to uncertainty in the broader macro environment, fiscal tightening, and tariff policies. No altcoin season index predicted this decline. They cannot, because they measure relative performance, not the underlying conditions that determine whether that performance is sustainable.
What to Watch Instead
A breadth index is a confirmation tool, not a leading indicator. It belongs at the end of a decision chain, not the beginning. The sequence that matters is:
1. Macro liquidity conditions. Is the dollar weakening? Are real rates declining? Is the NFCI below zero and falling? If not, any altcoin outperformance is likely a counter-trend rally within a hostile regime.
2. Bitcoin dominance trend. Is BTC.D below its 8-week moving average and declining? Historical data shows BTC dominance peaks precede every altseason by 2–6 months. If BTC.D is still rising, the rotation has not begun.
Source: Phemex: https://phemex.com/blogs/bitcoin-dominance-altcoin-season
3. ETH leadership. Is ETH/BTC above its 8-week moving average? Is ETH outperforming BTC over the trailing 4 weeks? CoinGecko’s altseason framework defines Phase 2 as the moment when ETH/BTC gains strength, signaling that capital is flowing from Bitcoin into Ethereum. Everything else follows.
4. Stablecoin supply and derivatives positioning. Is stablecoin market cap rising for 4 consecutive weeks? Is altcoin open interest dominance rising alongside alt market cap (not ahead of it)? Glassnode’s framework defines peak risk-on altseason as the phase where capital flows into both Ethereum and stablecoins are positive and increasing. When funding rates turn negative across major altcoins, as CoinDesk documented in March 2026, altcoins lead losses regardless of what the breadth index reads.
Source: Glassnode: https://insights.glassnode.com/the-week-onchain-week-41-2023/
5. Only then: breadth confirmation. The altcoin season index at 75+ confirms what the first four factors already indicated. It should never be the first signal — or the only one.
The Cardinal Rule
Never call broad altseason without breadth confirmation at 75+. But equally important: never trust breadth confirmation without the macro, dominance, ETH leadership, and liquidity preconditions in place. An altcoin season index above 75 during a tightening macro environment is not an opportunity — it is a trap.