What is the Altcoin Index?

The Altcoin Index is a market indicator that tracks how well top-performing altcoins have done compared to Bitcoin over a recent timeframe, usually the past 90 days. It returns a percentage score between 0 and 100, showing what share of these altcoins outperformed Bitcoin in that period.

A score of 100 means every altcoin in the sample beat Bitcoin’s returns, while a 0 means none did (e.g. a full-on altcoin takeover). Most of the time, the index falls somewhere in between, giving traders guidance into whether altcoins or Bitcoin are currently leading the market.

This metric acts as a snapshot of market momentum, helping investors identify shifting trends between Bitcoin and the broader altcoin market. By reflecting how capital rotates across crypto assets, the Altcoin Index offers a fast, intuitive view of where relative strength lies across coins.

How is the Altcoin Index Calculated?

The Altcoin Index is calculated by measuring how many top-performing altcoins have outpaced Bitcoin over the last 90 days. The result is expressed as a percentage and typically displayed as a chart to reflect trends over time. Here is how the index is constructed:

1. Select top altcoins: The index analyzes the top 50 (or 100) cryptocurrencies by market capitalization, excluding Bitcoin, to capture broad altcoin performance.
2. Set timeframe: A consistent 90-day rolling window is used to assess recent performance and allow for direct return comparisons.
3. Calculate altcoin returns: Each altcoin’s percentage change over the 90-day period is computed based on historical price data.
4. Compare with Bitcoin: These altcoin returns are then compared to Bitcoin’s return over the same window to identify outperformers.
5. Count outperformers: The number of altcoins with higher returns than Bitcoin is totaled to quantify market rotation toward alts.
6. Convert to percentage: This total is divided by number of alts used in the sample and multiplied by 100 to produce the index as a percentage score.
7. Visualize index: The final score (ranging from 0 to 100) is plotted over time in a chart format, allowing traders to track shifts in relative performance.

How to Read an Altcoin Index Chart

The Altcoin Index chart shows how altcoins have performed relative to Bitcoin over time, using a percentage score from 0 to 100. Traders use it to identify when capital is rotating into altcoins or staying with Bitcoin.

Here’s how to interpret key index levels:

1. 0-25 (Bitcoin Season): A low index means Bitcoin is outperforming most altcoins, BTC dominance is strong, and the market is in a risk-off mode.
2. 26-50 (Transition Phase): This range suggests Bitcoin still has the upper hand, but more altcoins are starting to gain relative strength.
3. 51-75 (Altcoin Season Approaching): Rising into this zone signals altcoins are gaining serious ground and could soon take over market leadership.
4. 76-100 (Altcoin Season): A score above 75 confirms that most altcoins are outperforming Bitcoin, marking a full risk-on shift in market sentiment.

For example, a reading of 80 means 80 percent of top altcoins outperformed Bitcoin over the last 90 days. A reading of 10 means the market is heavily BTC-led, with very few altcoins keeping up.

What Happens During an Altcoin Season?

When the Altcoin Index rises above 75, it signals that around three-fourths of top altcoins have outperformed Bitcoin over the last 90 days. This marks a full-on risk-on environment where altcoins are leading market gains and Bitcoin dominance is in decline.

In early 2018, the index surged well above that threshold as Ethereum, XRP, and Cardano saw triple-digit rallies while Bitcoin flattened out. It was a full-blown altcoin season, with broad outperformance across the altcoin market and capital rotating out of BTC.

The pattern repeated in early 2021, when Solana, BNB, and Polkadot gained over 300 percent in one quarter as Bitcoin traded mostly sideways. The index confirmed a broad-based shift, with altcoins collectively outperforming Bitcoin and taking over market leadership.

Most rencet breakout readings include late 2021 during the metaverse and Layer 2 boom, early 2022 as GameFi peaked, and two altseasons in 2024 driven by meme coins, Ethereum upgrades (Dencun), and DePIN narratives.

How to Use the Altcoin Index in Your Trading Strategy

Knowing what the Altcoin Index signals is one thing. Using that information profitably in live markets is something else entirely. Here are some example scenarios of using the index in action:

• Monitor it alongside other indicators: Always pair the Altcoin Index with Bitcoin dominance, volume, and price trends to get a full picture of where capital is moving.
• Use threshold levels as alerts: Index values above 50 or 75 suggest a shift toward altcoins, but don’t treat those numbers as hard trade triggers.
• Scale exposure in stages: I might rotate 20% into alts when the index crosses 50, then another chunk if it passes 75 with momentum.
• Watch for whipsaws near key levels: A short spike above 75 doesn't guarantee an altseason, especially if a few large caps are skewing the average.
• Track momentum, not just position: A steady rise from 20 to 60 is often more actionable than a flat reading at 75 with no follow-through.
• Align your allocation with context: If majors are leading during a 50–60 index reading, I’ll stick to large caps. If the index is over 80 and everything is running, small caps may come into play.
• Use the index to time exits too: When the index stalls at 85 or starts ticking down daily, that’s my signal to reduce exposure or lock in gains.
• Recognize overheating sentiment: If the market feels euphoric and the index is flashing extreme strength, I tighten up stops and start rotating defensively.
• Integrate with a broader toolkit: The index is a useful filter, but I always confirm it with onchain data, macro trends, technical levels, and narrative context.
• Remember it reflects the past: Since the index is based on 90-day performance, use it to confirm a developing trend, not to anticipate a reversal.

Best Altcoin Index Platforms

Several platforms track the Altcoin Index using similar logic: measuring how many top cryptocurrencies have outperformed Bitcoin over a recent period. While the goal is the same, each tool offers a unique mix of data scope, charting style, and use-case focus.

1. CoinMarketCap

CoinMarketCap calculates its Altcoin Index using the top 100 cryptocurrencies by market cap, excluding stablecoins and wrapped tokens, over a rolling 90-day window. The index shows the percentage of those coins outperforming Bitcoin, using the standard 75 percent threshold to signal altseason.

The platform features an interactive chart that displays historical index movements alongside Bitcoin dominance and other metrics. It’s deeply integrated into CMC’s broader ecosystem, making it easy to contextualize altseason data with market caps, trends, and individual coin stats.

CoinMarketCap’s index is ideal for users who want broad market coverage, reliable data, and familiar UX. However, it lacks multi-timeframe views (like 30-day or yearly indices) and depends entirely on CMC’s own coin ranking list, which can slightly affect inclusion.

2. CoinGlass

CoinGlass offers an Altcoin Season Index as part of its broader suite of trading analytics tools. While exact methodology details aren’t front and center, it likely uses a standard 90-day window and a top 50 or top 100 coin sample to determine how many alts are outperforming Bitcoin.

Its interface caters to data-heavy traders, with the index included in a “Market Cycle” section that also features open interest, funding rates, and liquidation data. Users can potentially layer the Altcoin Index with other trading signals, making it valuable for strategy confirmation.

CoinGlass stands out for its depth, allowing advanced users to cross-reference the index with futures activity or other market flows. Still, the platform assumes users know what they’re looking at, and its methodology isn’t as transparent as other options.

3. BlockchainCenter

BlockchainCenter is the original home of the “Altcoin Season Index” concept and remains a favorite for quick reads on the market cycle. It tracks the top 50 coins (excluding stablecoins and asset-backed tokens) and calculates what share outperformed Bitcoin over the past 90 days.

The site displays a static gauge that clearly states whether it’s “Altcoin Season” or “Bitcoin Season,” along with exact index value. It also includes a coin-by-coin breakdown and unique timeframes like Altcoin Month (30-day) and Altcoin Year (365-day) for additional perspective.

Traders love BlockchainCenter for its simplicity, clean logic, and fast clarity, as it tells you what you need to know at a glance. Its main tradeoff is scope: with only 50 coins and static visuals, it won’t catch every move or serve advanced data needs like CoinGlass.

Bitcoin Dominance and the Altcoin Index

It’s hard to talk about the Altcoin Index without mentioning Bitcoin dominance, which tracks Bitcoin’s share of total crypto market capitalization. These two indicators often move in opposite directions, making them two sides of the same market cycle.

One classic sign of altcoin season is Bitcoin dominance dropping significantly while many altcoins rally. This dynamic played out in 2017, when BTC dominance fell from 87 percent to 32 percent as capital rotated heavily into altcoins during the ICO boom.

Traders often watch both indicators together for confirmation. For example, if BTC dominance is trending down and the Altcoin Index rises from 40 to 60, that suggests a broad altcoin rally is forming. On the flip side, if dominance is rebounding and the index is stuck below 20, it's most like a Bitcoin season.

Limitations and Considerations

The Altcoin Index is a helpful signal for tracking market rotation, but it has limitations traders should keep in mind. It provides insight into recent performance, not future direction.

Considerations when using the Altcoin Index:

• Lagging indicator: The index calculates based on 90-day trailing returns, so it only reflects trends after they’ve taken shape, not before they begin.
• Coin sample differences: Depending on the platform, the sample may include the top 50 or top 100 coins, which affects how representative the reading truly is.
• No explanation of cause: The index tells you which coins outperformed Bitcoin but offers no further data whether it was due to hype, news, or fundamentals.
• Susceptible to outliers: A handful of soaring altcoins can skew the score higher, even if the majority of the altcoin market is moving sideways or struggling.
• Methodology variance: Platforms differ in how often they update the data, which assets they exclude, and what sources they use for pricing and rankings.
• Needs supporting tools: On its own, it’s incomplete and it's better pair it with technical analysis, BTC dominance, and macro sentiment to form a proper view.

Final Thoughts

The Altcoin Index is like a market weather report, letting you know if it’s Bitcoin season or if altcoins are running wild. For traders in the trenches, it’s a reliable tool to time rotations, rebalance portfolios, or just sanity-check market mood.

So keep one eye on the charts, one eye on the index, and remember, sometimes the smartest move is taking profits early and letting the last 10% for the next guy.