What Is Stock Market Seasonality?

Seasonality is the tendency for a market to do better or worse at certain times of the year. This page takes the S&P 500, an index of about 500 of the largest US companies, and groups its history by calendar month, so you can see how each January, each February and so on has done.

Since 1950, with dividends, the strongest months on average are January (+1.67%) and November (+1.61%). The weakest are October (+0.22%) and September (+0.23%).

Why might some months be stronger?

Nobody knows for sure. Common explanations include money arriving at the start of the year, tax-related selling near year-end, and lighter trading in late summer. These ideas are hard to prove, and a pattern can fade once people expect it.

Which page should I use?

This page: to see how each calendar month has done in the past.
S&P 500 Return calculator: to see what the index returned between any two months you pick.
Market Mood Index: to see how the market looks today, rather than what a time of year has usually brought.

How It's Calculated

A month's return compares its average price with the month before:

Monthly return = \frac{This month's index}{Last month's index} - 1

Then the page groups the returns by calendar month. For each month:

Average = \frac{Sum of that month's returns}{Number of years}

Years up = \frac{Years that month's return was above 0}{Number of years}

Example

The S&P 500's average price was 7,711.32 in the month before September 2026 and 7,631.47 in September 2026, so the price-only return was 7,631.47 ÷ 7,711.32 − 1 = -1.04%.

Why these numbers can differ from other sites

This page uses each month's average of daily closing prices, from Professor Robert Shiller's series. Many sites use the last close of each month. Averaging smooths the moves and spreads some of a sharp move into the next month, so a single month, and sometimes a month's rank, can look different. The median is the middle year's return, so one extreme year moves it far less than the average.

How to Use the S&P 500 Seasonality Page

"How has November usually gone for the S&P 500?" This page answers that. Since 1950, with dividends, it has averaged +1.61%, was up in 72% of years, and is the 2nd-strongest month.

Let's go through what you can choose and read. Everything is already filled in when the page opens:

Period: Pick Since 1950, Since 1871, Last 20 years or Last 10 years, which sets the years counted. Shorter periods reflect recent markets, but a few unusual years move them more.
Return type: Pick With dividends or Price only, which sets whether the dividends companies paid are counted. Price only runs a few months further, because dividend figures are published later.
Average return by month: one bar per month with its percentage, green above zero and red below. This month has a dark outline.
A typical year: the monthly averages built up from January, between lines that mark each month. Each dot shows the return so far that year. Steep parts are the stronger months and flat parts the weaker ones.
Monthly figures: under the line, each month's average, median, share of years up, best year and worst year.
Every month, year by year: each month's actual return, deeper green or red for bigger moves. It shows the last 20 years first. Click the button to see them all.
Share: the Facebook and X buttons share this page with a picture of the chart.

What History Shows

The pattern depends on the years you count. The strongest month is January since 1871 (+1.84%) and April over the last 20 years (+2.35%). March averaged +0.64% since 1950, but -0.74% over the last 20 years.

The differences are also small next to what can happen in any single year. January has the highest average since 1950, yet its best and worst years were +9.55% (1976) and -6.63% (2008).

Keep the limits in mind

Look at enough patterns in old data and some will appear by chance. Each month only has one result per year, so a handful of crashes or rebounds can shift an average. Results don't include taxes, fees or trading costs. A strong month in the past doesn't mean the next one will be strong.

Data Source

All data comes from Professor Robert Shiller's monthly S&P 500 series, which goes back to 1871. For the methodology, see chapter 26 of his book Market Volatility (Cambridge, MA: MIT Press, 1989). The return figures with dividends currently run through June 2026, and data starts in Jan 1871.

For information only. This is not investment advice or a recommendation to buy or sell anything at any time of year.