It always starts the same way. A few altcoins double within weeks, Ethereum and Solana pull ahead of Bitcoin, and the altcoin-season gauge jumps. If you hold mostly Bitcoin, you start asking whether to switch now.
The obvious answer is: if the season is starting, yes. The data says something else. The season usually does come. Switching on that day still left you behind Bitcoin almost every time.
Check 1: How broad is the move?
The usual test for altcoin season counts how many of the 50 largest altcoins beat Bitcoin over the last 90 days. From 75 percent it is called an altcoin season. Below 25 percent it is a Bitcoin season.
Example: on 1 September 2026 the share stood at 27.9 percent according to the Arena, on 2 October at 53.5 percent. Breadth had nearly doubled in four weeks.
Breadth shows whether a move is spreading. It does not show whether it will continue.
What happened in the past when breadth jumped like this?
What 13 earlier jumps show
For this piece, breadth was rebuilt from Binance daily prices since 2020, using the 50 most-traded altcoins. Every day on which the share rose above 50 percent after at least 30 days below it was counted. That happened 13 times. The rules were fixed before the first run.
| jump above 50 % | season within 90 days? | other altcoins vs BTC after 90 days | leaders vs BTC after 90 days | Bitcoin itself, 90 days |
|---|---|---|---|---|
| 10 Jun 2020 | yes | +13.9 % | +26.0 % | +2.4 % |
| 20 Jan 2021 | yes | +109.7 % | +20.3 % | +59.1 % |
| 20 Aug 2021 | yes | −18.0 % | +29.7 % | +15.3 % |
| 24 Apr 2022 | no | −20.8 % | −40.0 % | −43.1 % |
| 7 Aug 2022 | yes | −13.9 % | −0.7 % | −8.1 % |
| 7 Feb 2023 | no | −40.0 % | −44.7 % | +19.1 % |
| 8 Sep 2023 | no | −12.8 % | −21.6 % | +67.0 % |
| 11 Nov 2023 | yes | −9.4 % | −3.4 % | +26.9 % |
| 23 Oct 2024 | yes | −25.6 % | −46.9 % | +59.2 % |
| 10 Jun 2025 | yes | −1.9 % | −19.7 % | +1.6 % |
| 13 Jul 2025 | yes | −20.3 % | −38.0 % | −7.1 % |
| 8 Jan 2026 | no | −22.8 % | −6.2 % | −22.0 % |
| 8 May 2026 | no | −10.5 % | −29.4 % | −19.8 % |
Values are medians, each relative to Bitcoin. Leaders are the ten altcoins with the best 90-day record on the day of the jump, the other altcoins are the remaining 40.
In 8 of 13 cases a season followed, with the share rising above 75 percent within 90 days. The jump is usually a real start.
For the decision, though, the third column is what counts. In 11 of 13 cases, switching to altcoins meant falling behind Bitcoin, by a median of 13.9 percent after 90 days. The two exceptions came in 2020 and early 2021. Since August 2021 it happened every time, including the six cases in which a season followed.
The season usually comes. Switching on the gauge still loses to Bitcoin almost every time.
Why?
Why a season loses to Bitcoin
Breadth measures the past 90 days. When it reads high, the altcoins have already made their run. The season appears in the measurement only after it has already happened in the price.
That is not a flaw in the gauge. It describes what happened. Read as a start signal, though, it marks the end of the strongest stretch more often than its beginning.
The gauge tells you where the money went. It does not tell you where it goes next.
What would have to be added for switching to pay off?
Check 2: Is Bitcoin losing its lead?
If money really leaves Bitcoin, Bitcoin's share of the whole crypto market, its dominance, falls. That has to happen over weeks, not on single days.
Example: on 2 October 2026 dominance stood at 58.0 percent, against 58.7 percent a year earlier. Altcoins were rising without Bitcoin giving up share.
When many altcoins rise while Bitcoin holds its share, single coins are running. That is not a rotation.
Check 3: Is fresh money arriving?
Stablecoins are dollar tokens waiting to be spent in the crypto market. When their supply grows, buying power is added. When it shrinks, existing money is being moved around.
Example: according to DefiLlama, supply grew by $4.2 billion to $311.4 billion in the 30 days to 2 October 2026, faster than in the 30 days before. Against a total market of $2.9 trillion, that is a small inflow.
Without fresh money, every altcoin purchase has to come out of another coin, usually Bitcoin or the altcoins that have already run.
Check 4: Are you about to chase the winners?
When people switch, they usually want the coins that are already running. Measured across all days, that works against them. According to the Arena base rate, altcoins already in an uptrend against Bitcoin were a median 22.9 percent behind Bitcoin 90 days later. The average altcoin was 17.2 percent behind. That comes from 372 Binance pairs since 2018. The reason is the same as with breadth: by the time a trend is visible on the chart, it has usually been running for about 80 days.
At the 13 jumps themselves, the choice made little difference. The leaders were behind Bitcoin after 90 days in 10 of 13 cases, by a median of 19.7 percent. Against the rest they did worse in 8 cases and better in 5.
Leaders or laggards is the wrong question. On those days, both mostly lost to Bitcoin.
Check 5: Is a green light a buy signal?
Many gauges sum up the market in one colour. The Arena measured whether a green altcoin season helps as an entry filter. Across 27 strategies it helped 6 times, hurt 4 times and made no measurable difference 17 times (as of 28 September 2026).
A green light describes the market. It does not tell you which coin to buy.
The checks at a glance
| check | where to read it | speaks for switching | speaks against |
|---|---|---|---|
| 1 Breadth | Altcoin Season, share of top 50 ahead of Bitcoin | above 75 % and stable | jump from below, swings daily |
| 2 Leadership | Bitcoin dominance | falls over weeks | holds or rises |
| 3 Fresh money | stablecoin supply, 30 days | grows clearly | flat or shrinking |
| 4 Selection | the coin's trend against Bitcoin | – | coin is already visibly ahead |
| 5 Light | colour of the indicator | – | no measurable edge on its own |
None of the five checks is a buy signal on its own. Together they show whether a rotation from Bitcoin into altcoins is under way or whether only single coins are running.
The obvious objection
"Every altcoin season starts with a few coins. Wait for 75 percent and you are too late."
True, and that is exactly why the day of the jump above 50 percent was measured, not the day above 75. Even there, altcoins were mostly behind Bitcoin afterwards. Being early in a few coins is not the same as being early in a season. To be early, you would have to buy before the jump, and no gauge shows that.
What this means for you
If you hold Bitcoin and the gauge jumps: it is a description of the last 90 days. In 11 of 13 cases, holding did better than switching.
If you want altcoins anyway: first check whether Bitcoin's share falls over weeks and fresh money arrives. Without both, only a handful of coins is running.
If you want to buy single winners: the base rate speaks against coins that are already visibly ahead.
What remains open is whether breadth combined with falling dominance and growing stablecoins gives a better result. With 13 cases, that cannot be separated. It would be the next measurement once more cases exist.
How it was measured
Binance daily prices of all USDT pairs trading today, 1 January 2018 to 30 September 2026, excluding stablecoins, gold tokens, wrapped tokens and leveraged tokens. Universe on each day: the 50 pairs with the highest average trading volume over the last 30 days and at least 90 days of history. Breadth: the share of those with a better 90-day return than Bitcoin. Breadth can be computed from May 2020. Event: breadth rises above 50 percent after 30 days below it. Relative return: the altcoin's price change divided by Bitcoin's, without fees. Cross-check with 100 instead of 50 pairs: 9 events, a season in 6, other altcoins behind Bitcoin after 90 days in 8 of 9.
FAQ
Why trading volume instead of market value? Historical market values for all coins are not available as a free daily series, trading volume is. That is why this breadth differs slightly from the Arena gauge: 64 percent on 30 September 2026 against 53.5 percent on 2 October.
Are the results too pessimistic? If anything, too optimistic for altcoins. Only coins still trading today are counted. Coins delisted since are missing, and they would have pulled the altcoin side further down.
Do cases overlap? Two pairs are less than 90 days apart: September and November 2023, and June and July 2025. Without the later case of each pair, 9 of 11 are behind Bitcoin.
Not investment advice, not a recommendation, not a forecast — historical patterns are no guarantee.
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