Altcoin Season Index

The Altcoin Season Index plots a single 0–100 composite against the right axis — the share of the top-50 cryptoassets, with stablecoins and asset-backed tokens excluded, that have outperformed Bitcoin over the trailing 90 calendar days. Four tinted zones split the plot. Bitcoin Season sits at or below 25 in deep slate; the BTC-leaning band runs 25 to 49; altcoin-leaning runs 50 to 74; the rust-toned Altcoin Season zone sits at or above 75. Bitcoin’s USD price runs muted on the left log scale for cycle context.

The two exclusions are the point. Stablecoins are dropped because a token pegged to the dollar cannot meaningfully “outperform” or “underperform” a volatile asset — counting USDT would just measure Bitcoin’s own direction. Wrapped and staked derivatives (WBTC, stETH) are dropped because they are claims on assets already represented; counting them would double-vote. What is left is a clean tally of independent cryptoassets winning or losing a footrace against Bitcoin. Today’s reading is 50 — Altcoin-leaning — over a series of 3,343 daily observations stretching back to April 2017.

The methodology is short enough to quote intact. The canonical statement reads:

If 75% of the Top 50 coins performed better than Bitcoin over the last season (90 days) it is Altcoin Season.

With a single exclusion clause: Excluded from the Top 50 are Stablecoins (Tether, DAI…) and asset backed tokens (WBTC, stETH, cLINK,…). Cryptoasset markets clear continuously, so “90 days” is 90 calendar days, not 90 trading days. The Top 50 is rebalanced daily as market-cap ranks shift.

At any date t, the index is the share of the eligible sample whose return over the prior 90 days has beaten Bitcoin’s, multiplied by 100. The value rounds to the nearest integer when the sample size is exactly 50; in practice the eligible cohort drifts a few names around 50 as wrapped assets and new stablecoin issues enter and exit the top-cap list. We carry the daily index print from CoinGlass, which runs this construction; the formula and window choices we ship are documented on the methodology page.

The index reads rotation, not price. Sustained readings above 75 mark full altcoin seasons — risk-on capital spilling out of Bitcoin and down the cap stack. Sustained readings below 25 mark BTC-led regimes — capital consolidating into the most liquid asset, historically during late-bear capitulations and the opening leg of the next bull. Crossings of the 50 line are cosmetic handovers; the regime shifts that have actually mattered on the record happen at the 25 and 75 thresholds. A reading bouncing between 40 and 60 for months is not a signal — it is the index telling you no clean rotation is underway.

Reading the index against canonical cycle anchors surfaces the rotation pattern with no commentary needed. The 2017 ICO-mania alt-season peaked earlier in the year; by the December 2017 price top the index had already collapsed into the BTC-leaning band — alts had rolled over weeks before Bitcoin did. The 2018 cycle low sat deep in BTC Season as alts capitulated harder than BTC. The May 2021 altseason peak printed near the very top of the scale; the November 2021 cycle top was a quieter altcoin regime by comparison; the 2022 post-FTX low sat in the BTC-leaning band, never reaching the sub-25 BTC Season floor. Read the exact prints in the table below; the full anchor list:

A different cut of the same data: how many days each cycle has spent in each zone. The index series begins April 2017, so the 2012 and 2016 halving cycles predate coverage. We anchor cycles on the 2020 and 2024 halving block-confirmation days — block 630,000 on 2020-05-11 and block 840,000 on 2024-04-20 UTC. The pattern is asymmetric and worth pausing on: the BTC-leaning and BTC-Season bands together host most of the days in every cycle, and full Altcoin Season — the 75+ band — is the smallest zone in absolute terms. The phrase “altcoin season” gets thrown around as though it were a recurring season like winter; the time-in-zone table is the reminder that the 75+ regime accounts for roughly 13% of all days on record — and as little as a single-digit share of the current cycle.

One of the things this chart does not advertise is that “the Altcoin Season Index” refers to a methodology, not a single canonical reading. The 75-of-50 construction was popularised by blockchaincenter.net, and a top-100 variant runs on CoinMarketCap’s panel. The two implementations agree on the threshold (75%) and the window (90 days) but disagree on the basket.

The disagreement matters most in transitions. When the 51st–100th-cap cohort outperforms the top-50 — the usual mid-cap-front-running pattern early in a rotation — the top-100 index turns altcoin-season first. When the 51st–100th-cap cohort underperforms (early-bear trash-take selloffs), the top-100 index decays first. Same threshold, same window, different reading on the same day. We ship the top-50 form because the canonical definition specifies “Top 50” in plain text; readers cross-checking against the top-100 panel will see a different number with a parallel meaning.

The Top-50 universe also drifts cycle-over-cycle. In 2021 the sample leaned heavily DeFi (UNI, AAVE, COMP) and meme-tokens (DOGE, SHIB); in 2024 the sample leaned L1-infrastructure and restaking (SOL, AVAX, ETH-restakers). Comparisons across cycles are sample-robust but not cohort-identical — what counts as a top-50 altcoin in 2026 is not what counted in 2021.

The 90-day window lags meaningful regime shifts by 30–60 days. The index is a backward-looking 90-day rolling counter; rotations show up in smaller-cap market-cap aggregates and in the dominance line weeks before the trailing-90-day return calculation can register. The clearest case is early 2021: through November and December 2020 the index actually sat deep in BTC Season — single digits at one point — because Bitcoin’s run to fresh highs was outrunning the alt complex on the trailing 90 days. Only once the ETH and DeFi rotation had been running for weeks did the index climb back through the leaning bands in February and March 2021, lagging a move that had already begun. Treat the index’s climb as confirmation, not a trigger; the leading edge of rotation lives elsewhere.

Late-bull blow-off tops are an inverted trap. The November 2021 cycle top is the cautionary case. Because the 90-day window still carried the violent May 2021 alt drawdown in its lookback, the index printed a quieter altcoin reading at the actual November high than it had at the May local top — even though that was the cycle’s last and largest distribution window. A reading falling out of Altcoin Season is not proof rotation is over; it can simply mean the window has rolled past the leg that drove the score.

Top-50 versus top-100 basket sizing produces different readings. The canonical 75-of-50 form and the top-100 variant can disagree by 10–20 points during transitions. We ship the top-50 form because the canonical definition specifies it; the top-100 panel will print a different number on the same day with a parallel meaning. Read either; do not splice the two.

Stablecoin issuance moves dominance but not this chart. Bitcoin Dominance reacts mechanically to stablecoin mints and burns — the stablecoin slug sits in dominance’s denominator. The Altcoin Season Index excludes stablecoins entirely, so a multi-billion-dollar USDT issuance on a quiet weekend rotates dominance without touching this index. The two charts agree most when the rotation is altcoin-driven; they disagree most when the move is stablecoin-driven. When they disagree, the disagreement is the signal — check the stablecoin float before reading either as a rotation call.

If you accumulate on a schedule, this chart asks nothing of you. The index is a cohort-rotation gauge measured against Bitcoin; a steady weekly buy operates below its timescale. Skim the regime line for cycle texture — a sustained sub-25 print is decent company for accumulation — but there is no entry here to time.

If you are timing the cycle, the two thresholds do different jobs. Treat the 75 crossing as a confirmation that an alt rotation has been underway for weeks, not a trigger that one is about to begin — the OTHERS market-cap line and the Bitcoin Dominance reading move earlier. The 25 crossing is the cleaner setup: sustained readings below 25 have bracketed every cycle-bottom window on the index’s record, and being a lagging indicator hurts you far less when you are buying a base than when you are chasing a top. Pair either with the stablecoin float for the dry-powder view.