September is bitcoin's worst month, and the last three were green

Every September a version of the same sentence goes round the market: this is bitcoin's worst month. We counted, using monthly candles from Binance back to 2017, and the claim is half true in a way that matters.

What bitcoin in September has actually done:

• 2017 to 2022: six Septembers, six of them red, from minus 3.1% to minus 13.6%.
• 2023, 2024, 2025: plus 3.9%, plus 7.4%, plus 5.4%. Three green Septembers in a row.
• Across all nine: an average of minus 3.0% and a median of minus 5.5%.
• Every other month of the year: an average of plus 5.3%, with 45% of them red against September's 67%.

So the seasonal rule is real and it is also stale. It was built entirely on the 2017 to 2022 stretch, and it has been wrong three years running. Anyone quoting the average without the last three years is quoting a number that stopped describing the market in 2023.

This September is running at minus 2.1% so far, from an opening of $78,581 to $76,897 as we write. That is the fourth-mildest of the nine on the negative side, and eighteen days of the month are still to come.

What traders are actually watching

The traders being quoted this week are not talking about seasonality at all. They are talking about one meeting.

“Markets are already positioned for a more hawkish Fed and a likely rate increase.”

— Joel Kruger, LMAX Group, 11 September 2026

Joel Kruger, LMAX Group, quoted by CoinDesk, 11 September 2026

Bitget analyst Lewis Huang named the level that matters on the way down before yesterday's data: $76,270, which bitcoin has not traded below since the August rally began. It sits within about a thousand dollars of the current price, and yesterday's release hour alone covered $1,283.

Three dates that decide the month

Three dates decide the rest of the month, and they are close together.

Today at 12:30 UTC: August consumer prices, expected at 3.4% headline and 2.4% core. We set out the asymmetry this morning: a rate rise is already about 70% priced, so a soft print has more room to move than a hot one.

Monday 15 September: the Senate's procedural vote on the CLARITY Act, which needs sixty votes and would hand the SEC and CFTC the job of writing rules for DeFi operators. Then 15 and 16 September: the Federal Reserve meeting that the futures are pricing.

Two scenarios, held at once

Two scenarios worth holding at once. If CPI lands hot and the Fed raises, the market has largely paid for that already, and the move is likely smaller than the headlines will suggest. If CPI lands soft, the position unwinds, and unwinding is what produces the bigger candle in either direction.

The tell will be breadth rather than price. Yesterday the CoinDesk 20 fell 3% against bitcoin's 2%, and every name on the losers list was still up over thirty days. If that repeats, the selling is macro and September closes closer to flat than to the 2019 pattern.

Nothing here should be taken as financial advice; treat it as information to consider.