Everyone wants to know when altseason starts. Most people look at price for the answer. I look at the money waiting to be spent first.

That money is stablecoins: dollars parked on-chain in USDT, USDC and the rest. When stablecoin supply grows fast, new cash is arriving in crypto with nowhere to go yet. Some of it ends up in Bitcoin. In the big altseasons, a lot of it went further out.

No fuel, no altseason

Here is the record, weekly, from February 2017 to May 2026. We measured stablecoin supply against its level 13 weeks earlier, then checked whether Bitcoin's share of the crypto market fell 10 points or more over the next six months. That fall is what an altseason looks like in the data.

  • Stablecoin supply up 10% or more in 13 weeks: Bitcoin's share fell 10 points or more within six months in 73 of 289 weeks.
  • Under 10%: it happened in 0 of 194 weeks.

Read that the right way round. Fast stablecoin growth did not guarantee an altseason. Three times out of four it came to nothing. But in nine years there was never an altseason without it. It is the fuel, not the spark.

When the fuel lit

DeFi summer, 2020. Stablecoin supply went from $9.8bn in early May to $17.3bn by early September. Bitcoin's share fell from 68% to 58%, and DeFi coins had their run.

The 2020-21 altseason. Supply went from $32.3bn in early January 2021 to $94.7bn by mid-May. At the peak it was growing 140% in 13 weeks. Bitcoin's share fell from 69% to 41%. That was the biggest altseason since 2017.

When it did not

2019. Stablecoins grew fast here too, at times more than 60% in 13 weeks. Bitcoin took the money. Its share climbed from 53% in March to 72% in September. Fuel on, no altseason.

2023 to 2024. Supply grew from $124bn to $198bn, which sounds like a lot. But it grew slowly and never reached 20% in 13 weeks. Bitcoin's share never fell below 51%. Real yields (the 10-year US inflation-linked yield) sat between 1.6% and 2.5%. In 2020-21 they were negative, between -1.1% and -0.4%. Cash that earns a real return outside crypto is in less of a hurry to take risk.

What this tells you, and what it does not

Stablecoin fuel tells you whether an altseason is possible. It does not tell you when it starts, which coins lead, or how far it goes. The speed of growth matters more than the size. A big total that grows slowly did nothing in 2023 and 2024.

That is why we never read it alone. On our Altseason page it is one of six fuel signs, next to real yields, risk appetite, how many coins are in profit and how fast the whole market is moving. We track all six every week, against every altseason since 2016.

Alpha Insider

Is the fuel on right now?

The Altseason page shows all six fuel signs every week, and which past season today looks most like. Alpha Insider members also get The Tape, our live order-book tool.

See the plans

Sources: stablecoin supply from DefiLlama (USDT from TradingView before April 2020, when DefiLlama undercounts it); Bitcoin's market share from CoinGecko; real yields from FRED (10-year TIPS). Weekly data. Counts are past weeks, not a forecast.

This post is education and research, not financial advice. Crypto is volatile and you can lose all of the money you put in. Past patterns, including the record above, do not predict what happens next. Do your own research and make your own decisions.