An Altcoin Season Index measures breadth: how many eligible altcoins outperformed Bitcoin over a stated window. It asks whether relative strength is widespread or concentrated in a few names.

There is no single universal index. CoinMarketCap currently uses the top 100 eligible coins over 90 days, while BlockchainCenter uses the top 50; both exclude stablecoins and asset-backed tokens and use a 75% threshold for “altcoin season”.

How the index is calculated

Each eligible asset is compared with Bitcoin over the provider’s lookback window, commonly 90 days. The score is the share of the sample that beat Bitcoin, usually scaled from 0 to 100.

Each asset gets one vote, so the measure captures breadth rather than market-cap-weighted performance. The OCM chart must state its provider, universe, exclusions and threshold.

What a high reading means

A high reading means most eligible assets in that version of the index have outperformed Bitcoin over the lookback. It describes a broad relative move that has already happened.

It does not say the assets rose in dollar terms: an altcoin can outperform Bitcoin by falling less. Read the score with absolute returns and total market direction.

What it does not tell you

The index does not measure project quality, liquidity or investability. A token counts once if it is eligible, regardless of those differences.

The sample also changes as rankings and eligibility change. Historical readings therefore compare evolving universes, not a fixed basket.

How to read it

Altcoin season. The provider’s stated supermajority of eligible assets has outperformed Bitcoin.

Broad altcoin outperformance. More eligible assets are beating Bitcoin, but the formal threshold may not be met.

Mixed. No broad relative-performance regime.

Bitcoin season. Few eligible altcoins are outperforming Bitcoin under the provider’s rules.

The Altcoin Season Index sits inside the Relative Performance dashboard. Its methodology label should stay visible beside the chart.

Common questions

How is this different from Bitcoin Dominance?

Dominance is market-cap weighted. An Altcoin Season Index usually gives each eligible asset one vote, making it a breadth measure.

Why 90 days?

It is a common convention, not a universal rule. Some providers offer other windows, which will produce different readings.

Does a high score mean altcoins rose?

No. They only need to outperform Bitcoin. In a falling market, that can mean losing less.

Does it account for quality?

No. Eligibility and ranking rules determine the sample; the score does not assess fundamentals.

Why can providers disagree?

They may use different sample sizes, exclusions, data cut-offs and thresholds. Name the source before comparing a score.