September Was Against the Tide: Why Not Trust the Market's "Clock"
5 minReading time
Published Oct 6, 2025
September Was Against the Tide: Why Not to Trust the Market's 'Clock'
September is historically considered the worst month for the stock market. On average, the S&P 500 tends to lose about 1% of its value during this period, which has created the superstition that, after summer, investors should sell their stocks and wait for a decline.
But this year, the exact opposite happened: the market rose more than 3.5% in September. This reminds us of an important lesson: markets are driven by economic fundamentals and corporate results — not by dates on the calendar.
What is the 'September Effect'
The so-called September Effect is based on statistics. Traditionally, it is seen as the weakest month of the year for stock markets — the only one in which, historically, indices closed lower more than half the time (about 55%).
Possible explanations for the phenomenon
Fund managers returning from vacation and rebalancing portfolios.
Profit-taking after accumulated gains.
Closing of fiscal cycles, such as hedge funds closing the year in September and making adjustments.
Fixed income market more active during this period, attracting resources that could be in stocks.
Although all these theories make sense, this year showed that blindly trusting seasonal patterns can be dangerous. The market can move in the opposite direction of what is expected.
September is just one of the dangerous months to try to predict the market. The others are: October, November, December, January, February, March, April, May, June, July, and August.
September Was Against the Tide: Why Not to Trust the Market's 'Clock'
September is historically considered the worst month for the stock market. On average, the S&P 500 tends to lose about 1% of its value during this period, which has created the superstition that, after summer, investors should sell their stocks and wait for a decline.
But this year, the exact opposite happened: the market rose more than 3.5% in September. This reminds us of an important lesson: markets are driven by economic fundamentals and corporate results — not by dates on the calendar.
What is the 'September Effect'
The so-called September Effect is based on statistics. Traditionally, it is seen as the weakest month of the year for stock markets — the only one in which, historically, indices closed lower more than half the time (about 55%).
Possible explanations for the phenomenon
Fund managers returning from vacation and rebalancing portfolios.
Profit-taking after accumulated gains.
Closing of fiscal cycles, such as hedge funds closing the year in September and making adjustments.
Fixed income market more active during this period, attracting resources that could be in stocks.
Although all these theories make sense, this year showed that blindly trusting seasonal patterns can be dangerous. The market can move in the opposite direction of what is expected.
September is just one of the dangerous months to try to predict the market. The others are: October, November, December, January, February, March, April, May, June, July, and August.
Where is the Market Really Going?
Despite the uncertainties, the long-term growth trend remains solid. In September, the Federal Reserve (Fed) cut interest rates for the first time in almost a year and indicated that it will continue to do so — historically, a positive sign for the stock market.
Furthermore:
There were announced billion-dollar investments in the artificial intelligence sector, reinforcing confidence in innovation.
Economic data came in relatively positive, supporting the continuation of stock price appreciation.
The result: September, which in theory should be a weak month, became one of the best of the year.
The Lesson from September: Timing Doesn't Work
The performance of September reinforces a key investment principle: trying to predict the exact timing of the market rarely works.
The true path to success is investing regularly.
Having patience and a long-term horizon is much more effective than following seasonal superstitions.
Consistent strategies outperform bets on specific dates.
September is proof that consistent results come from discipline, not from trying to guess short-term movements. - Mark T. Grills; S&P500 Journal
Market Reviews are at Kyvoo
The “September Effect” may be a statistical curiosity, but it should not guide financial decisions. In 2025, we saw just the opposite of what was expected: the market rose when most believed it would fall.
The lesson is clear: invest consistently, focus on the long term, and base it on real fundamentals.
Visual Container: [For those looking to take their first steps or test strategies safely, Kyvoo offers an accessible platform, with over 100 assets and a free demo account. This way, you can learn in practice how to build consistency in the market without relying on seasonalities.
Market Reviews are at Kyvoo
The “September Effect” may be a statistical curiosity, but it should not guide financial decisions. In 2025, we saw just the opposite of what was expected: the market rose when most believed it would fall.
The lesson is clear: invest consistently, focus on the long term, and base it on real fundamentals.
Visual Container: [For those looking to take their first steps or test strategies safely, Kyvoo offers an accessible platform, with over 100 assets and a free demo account. This way, you can learn in practice how to build consistency in the market without relying on seasonalities.
Finance
Finance
Finance
Finance
September Was Against the Tide: Why Not to Trust the Market's 'Clock'
September is historically considered the worst month for the stock market. On average, the S&P 500 tends to lose about 1% of its value during this period, which has created the superstition that, after summer, investors should sell their stocks and wait for a decline.
But this year, the exact opposite happened: the market rose more than 3.5% in September. This reminds us of an important lesson: markets are driven by economic fundamentals and corporate results — not by dates on the calendar.
What is the 'September Effect'
The so-called September Effect is based on statistics. Traditionally, it is seen as the weakest month of the year for stock markets — the only one in which, historically, indices closed lower more than half the time (about 55%).
Possible explanations for the phenomenon
Fund managers returning from vacation and rebalancing portfolios.
Profit-taking after accumulated gains.
Closing of fiscal cycles, such as hedge funds closing the year in September and making adjustments.
Fixed income market more active during this period, attracting resources that could be in stocks.
Although all these theories make sense, this year showed that blindly trusting seasonal patterns can be dangerous. The market can move in the opposite direction of what is expected.
September is just one of the dangerous months to try to predict the market. The others are: October, November, December, January, February, March, April, May, June, July, and August.
Where is the Market Really Going?
Despite the uncertainties, the long-term growth trend remains solid. In September, the Federal Reserve (Fed) cut interest rates for the first time in almost a year and indicated that it will continue to do so — historically, a positive sign for the stock market.
Furthermore:
There were announced billion-dollar investments in the artificial intelligence sector, reinforcing confidence in innovation.
Economic data came in relatively positive, supporting the continuation of stock price appreciation.
The result: September, which in theory should be a weak month, became one of the best of the year.
The Lesson from September: Timing Doesn't Work
The performance of September reinforces a key investment principle: trying to predict the exact timing of the market rarely works.
The true path to success is investing regularly.
Having patience and a long-term horizon is much more effective than following seasonal superstitions.
Consistent strategies outperform bets on specific dates.
September is proof that consistent results come from discipline, not from trying to guess short-term movements. - Mark T. Grills; S&P500 Journal
Don't miss out
Glory follows the hero
The rewards come with fame!
Market Reviews are at Kyvoo
The “September Effect” may be a statistical curiosity, but it should not guide financial decisions. In 2025, we saw just the opposite of what was expected: the market rose when most believed it would fall.
The lesson is clear: invest consistently, focus on the long term, and base it on real fundamentals.
Visual Container: [For those looking to take their first steps or test strategies safely, Kyvoo offers an accessible platform, with over 100 assets and a free demo account. This way, you can learn in practice how to build consistency in the market without relying on seasonalities.