Alt Season Index: Measuring When Capital Rotates from Bitcoin to Altcoins

What the Alt Season Index Measures

The index is calculated by checking what percentage of the top N altcoins (usually top 50 or 100) outperformed Bitcoin over the past 90 days:

Alt Season Index = (Alts outperforming BTC in 90 days) / (Total alts compared) × 100

If 80 of 100 tracked altcoins outperformed BTC over 90 days, the index is 80. If only 15 outperformed, the index is 15.

Thresholds:

• Above 75: "Alt season" - clear altcoin outperformance regime
• 50-75: Mixed / altcoin dominance modest
• 25-50: Bitcoin-leading market
• Below 25: "Bitcoin season" - BTC dramatically outperforming alts

Historical Alt Season Patterns

The Classic Rotation

In previous cycles (2017, 2021), alt seasons followed a characteristic pattern:

1. BTC leads the cycle off the bottom: Bitcoin dominance rises as BTC rallies while alts are still depressed. Index is very low (below 20).
2. BTC extends rally; ETH catches up: Ethereum begins outperforming BTC. Dominance peaks and starts rolling over. Index climbs from low teens to 30-50.
3. Large caps run: Top-20 altcoins begin outperforming BTC. Index climbs through 50-70.
4. Mid-caps run: Mid-cap altcoins (rank 20-100) outperform. Index climbs above 75.
5. Small-caps run: Small-caps and memecoins run parabolically. Index can reach 80-90+.
6. Cycle top: Parabolic alt action signals late-cycle distribution. Index peaks as BTC and ETH begin underperforming on a relative basis.
7. Bear market: capital rotates back to BTC and stablecoins. Index collapses.

2024-2026: Pattern Shifts

The classic pattern has shifted in recent cycles:

• ETF flows: Bitcoin and Ethereum spot ETFs have concentrated institutional capital in BTC and ETH, delaying rotation into smaller alts
• Solana ecosystem: Solana's rise as a consumer-app L1 has produced alt outperformance outside the traditional top-10 without preceding a broad alt season
• Memecoins vs utility tokens: memecoin speculation has decoupled from ecosystem-token appreciation in ways that complicate the index
• Institutional selectivity: institutions buy BTC, ETH, and a few majors; they rarely rotate into speculative small-caps. This has dampened small-cap alt seasons.

BTC Dominance as a Companion

The Alt Season Index is complementary to Bitcoin dominance. The relationship:

• BTC dominance trending down + Alt Season Index climbing = capital rotating from BTC to alts
• BTC dominance trending up + Alt Season Index falling = capital rotating from alts back to BTC
• BTC dominance flat + Alt Season Index volatile = mixed regime; specific narratives driving individual alts without broad rotation

Watching both together provides a clearer picture than either alone.

What Alt Season Means for Traders

Portfolio Allocation

Alt season regime can inform allocation:

• Bitcoin season (Index < 25): overweight BTC, underweight alts. Cash or stablecoins for dry powder.
• Mixed (Index 25-50): balanced BTC/ETH/stablecoins/high-conviction alts.
• Early alt season (50-75): rotate toward large-cap alts, reduce BTC overweight.
• Full alt season (>75): speculation-friendly regime; size alt exposure higher. But prepare for cycle-top conditions.

Timing Rotations

Rotating too early (while BTC is still leading) leaves money on the table in the BTC rally. Rotating too late (after alt season is mature) catches the top.

The index helps identify regime shifts. When the index crosses specific thresholds (notably moving above 50 from below, or above 75), the regime is shifting enough to warrant allocation changes.

Exit Timing

Full alt season (Index above 80) combined with other cycle-top signals (high MVRV, high Puell, extreme funding rates) has historically been a cycle-top zone. Exit timing into alt season peaks has been profitable even without perfect top-picking.

Limitations

• Lagging: 90-day window means the index confirms regime change after it's underway. Faster-window variants exist but are noisier.
• Index composition: which alts are in the "top 100" changes over time. Churn in the composition affects signal.
• Excludes stablecoins and wrapped: appropriate exclusion but means certain large-cap assets aren't counted.
• Pattern shifts: as noted above, 2024-2026 has had structural shifts in how alt seasons unfold.

Related Intelligence

• Bitcoin dominance: Complementary measure of BTC's market share relative to alts.
• Fear and Greed Index: Broader sentiment gauge that often moves with alt season stages.
• MVRV ratio: On-chain cycle indicator that pairs with alt season timing.