What is the seasonality effect in markets?
The seasonality effect is the tendency of a market to move the same way at the same time of year, more often than chance would suggest. Natural gas around the heating season, grains around the harvest and stocks around the turn of the year are well known examples. Seasonality describes the past; it is never a forecast.
Why seasonal patterns exist
Commodities have the clearest reasons. Demand for heating fuels rises before winter, gasoline demand peaks in the driving season, and grain supply swings with planting and harvest. See the commodity season calendar.
Stocks have softer reasons that are often cited: money flowing in at the start of the year, tax-related selling near year-end, funds rebalancing at quarter ends, and thin holiday trading. The best known of these are tested in our calendar studies.
Currencies and rates react to year-end funding needs and central bank calendars. Crypto has a short history, so its patterns rest on few years and deserve extra caution.
How we measure it
- Month by month. For each market and calendar month: average and median move, share of up years, best and worst year. See seasonality by month.
- Pattern rating. Strong, moderate, weak or no clear pattern, based on whether the month beats the market's own average month and held in both halves of the history.
- Seasonal windows. Exact date ranges, picked on older years and kept only if they also held in the last 10 years. We publish 138 of them on the windows page.
- Ahead or behind the season. This year's move against where a typical year stood on the same date: seasonal gaps.
The strongest monthly patterns in our data
| Market | Month | Average | Up years | Years |
|---|---|---|---|---|
| Alphabet | October | +8.69% | 73% | 22 |
| Sugar | March | -6.19% | 31% | 26 |
| Siemens | November | +5.56% | 83% | 29 |
| Corn | December | +5.45% | 85% | 26 |
| Palladium | December | +4.76% | 68% | 28 |
| Nickel | January | +4.76% | 71% | 34 |
| Allianz | November | +4.24% | 76% | 29 |
| Cotton | December | +3.70% | 69% | 26 |
| Platinum | January | +3.39% | 76% | 29 |
| Silver | June | -2.96% | 31% | 26 |
| Dow Jones Industrial Average | November | +2.69% | 76% | 34 |
| Nestlé | April | +2.27% | 78% | 37 |
Months rated strong, with 20 years of data or more, as of October 16, 2026.
Traps to avoid
- Data mining. Test enough date ranges and some will look perfect by luck. That is why our windows are checked on years they were not picked from.
- Small samples. Ten years of data can produce a 70% hit rate by chance. We cap the rating of short histories.
- Averages hide outliers. One extreme year can make a month look strong. Compare the average with the median.
- Patterns fade. A well known pattern can weaken once many people trade on it. We show older and recent decades side by side.
Questions
What is the seasonality effect in markets?
It is the tendency of some markets to move in the same direction at the same time of year, more often than chance would suggest. Examples are natural gas around the heating season, grains around the harvest and stock indices around the turn of the year.
Is market seasonality real?
Some patterns have held across many decades and in both halves of the history, which makes pure luck less likely. Many others are weak or disappear in recent years. The honest test is how a pattern did in years that were not used to find it.
Why do seasonal patterns exist?
Explanations commonly given include supply and demand cycles in commodities (harvests, heating and driving seasons), money flows in stocks (year-end bonuses, tax-related selling, fund rebalancing) and holiday effects on trading volume.
Can seasonality predict prices?
No. Seasonality describes what usually happened in the past. A strong month still has losing years, and news can overwhelm any seasonal tendency. We show the record and the exceptions, never a forecast.
How do you measure seasonality?
We compute every calendar month's average and median move, the share of up years and whether the month differs from the market's own average month. Seasonal windows are picked on older years and kept only if they also held in the last 10 years.
History describes tendencies, not a forecast. Not investment advice. How to read the numbers · Methodology
Not investment advice. Market Seasonality publishes historical statistics, news summaries and scenario analysis for information and education. Past patterns do not guarantee future results. Nothing here is a recommendation to buy, sell or hold any asset, and scenarios describe possible paths without predicting them. See the disclaimer and methodology.