Does Biogen (BIIB) stock go up or down depending on the month?
Biogen month by month, year by year
| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2026 | +2.2% | +6.6% | -4.4% | +3.2% | +3.6% | +10.2% | -6.1% | |||||
| 2025 | -5.9% | -2.4% | -2.6% | -11.5% | +7.2% | -3.2% | +1.9% | +3.3% | +5.9% | +10.1% | +18.0% | -3.3% |
| 2024 | -4.7% | -12.0% | -0.6% | -0.4% | +4.7% | +3.1% | -8.0% | -4.0% | -5.3% | -10.2% | -7.7% | -4.8% |
| 2023 | +5.0% | -7.2% | +3.0% | +9.4% | -2.6% | -3.9% | -5.1% | -1.0% | -3.9% | -7.6% | -1.5% | +10.5% |
| 2022 | -5.8% | -6.6% | -0.2% | -1.5% | -3.6% | +2.0% | +5.5% | -9.2% | +36.7% | +6.2% | +7.7% | -9.3% |
| 2021 | +15.4% | -3.4% | +2.5% | -4.4% | +0.1% | +29.5% | -5.6% | +3.7% | -16.5% | -5.8% | -11.6% | +1.8% |
| 2020 | -9.4% | +14.7% | +2.6% | -6.2% | +3.5% | -12.9% | +2.7% | +4.7% | -1.4% | -11.1% | -4.7% | +2.0% |
| 2019 | +10.9% | -1.7% | -27.9% | -3.0% | -4.3% | +6.6% | +1.7% | -7.6% | +5.9% | +28.3% | +0.4% | -1.0% |
| 2018 | +9.2% | -16.9% | -5.2% | -0.1% | +7.4% | -1.3% | +15.2% | +5.7% | -0.1% | -13.9% | +9.7% | -9.8% |
| 2017 | -2.2% | +4.1% | -5.3% | -0.8% | -8.6% | +9.5% | +6.7% | +9.3% | -1.1% | -0.5% | +3.4% | -1.1% |
| 2016 | -10.9% | -5.0% | +0.3% | +5.6% | +5.4% | -16.5% | +19.9% | +5.4% | +2.4% | -10.5% | +5.0% | -3.6% |
| 2015 | +14.6% | +5.2% | +3.1% | -11.4% | +6.2% | +1.8% | -21.1% | -6.7% | -1.8% | -0.4% | -1.3% | +6.8% |
| 2014 | +11.8% | +9.0% | -10.2% | -6.1% | +11.2% | -1.3% | +6.1% | +2.6% | -3.6% | -2.9% | -4.2% | +10.3% |
| 2013 | +6.6% | +15.8% | +13.7% | +8.5% | -9.4% | +1.4% | -2.3% | +13.0% | +1.4% | +19.2% | -3.9% | |
| Average | +2.3% | -0.7% | -2.1% | -1.0% | +2.8% | +1.0% | +1.1% | +0.3% | +2.3% | -1.3% | +2.5% | -0.4% |
| % of years up | 54% | 43% | 43% | 29% | 71% | 50% | 64% | 54% | 38% | 31% | 54% | 38% |
| Years observed | 13 | 14 | 14 | 14 | 14 | 14 | 14 | 13 | 13 | 13 | 13 | 13 |
Biogen month by month: the summary
Over 2013-2026, here's what Biogen (BIIB) stock did each month, on average: January +2.3% (up 54% of 13 years), February -0.7% (up 43% of 14 years), March -2.1% (up 43% of 14 years), April -1.0% (up 29% of 14 years), May +2.8% (up 71% of 14 years), June +1.0% (up 50% of 14 years), July +1.1% (up 64% of 14 years), August +0.3% (up 54% of 13 years), September +2.3% (up 38% of 13 years), October -1.3% (up 31% of 13 years), November +2.5% (up 54% of 13 years), December -0.4% (up 38% of 13 years). In other words, BIIB historically rose in January, May, June, July, August, September, November, and fell in February, March, April, October, December.
Does Biogen really go up in May?
Over 2013-2026, May is Biogen's strongest month: +2.8% on average, positive in 10 of 14 years. At the other end, March shows -2.1%. But a monthly gap is often built on one or two extreme years — the table above shows it: look at the spread, not just the average. Seasonality only means something when it has a cause (selling season, earnings calendar, year-end tax effects); with no identified cause, it's probably noise.
Frequently asked questions
Does Biogen stock go up or down in August?
Over 13 years, BIIB rose +0.3% on average in August, finishing the month up 7 times out of 13 (54%). Median: +2.6%. Results are split year to year — there's no clear pattern. ⚠️ 13 years of data is not a prediction.
Does Biogen stock go up or down in November?
Over 13 years, BIIB rose +2.5% on average in November, finishing the month up 7 times out of 13 (54%). Median: +0.4%. Results are split year to year — there's no clear pattern. ⚠️ 13 years of data is not a prediction.
Does Biogen stock go up or down in January?
Over 13 years, BIIB rose +2.3% on average in January, finishing the month up 7 times out of 13 (54%). Median: +2.2%. Results are split year to year — there's no clear pattern. ⚠️ 13 years of data is not a prediction.
Does Biogen stock go up or down in September?
Over 13 years, BIIB rose +2.3% on average in September, finishing the month up 5 times out of 13 (38%). Median: -1.1%. Results are split year to year — there's no clear pattern. ⚠️ 13 years of data is not a prediction.
Does Biogen stock go up or down in October?
Over 13 years, BIIB fell -1.3% on average in October, finishing the month up 4 times out of 13 (31%). Median: -2.9%. It's one of its weakest months. ⚠️ 13 years of data is not a prediction.
Does Biogen stock go up or down in July?
Over 14 years, BIIB rose +1.1% on average in July, finishing the month up 9 times out of 14 (64%). Median: +1.8%. Results are split year to year — there's no clear pattern. ⚠️ 14 years of data is not a prediction.
What is the best month to buy Biogen stock?
Historically, May: over the last 14 years, BIIB gained +2.8% on average that month and finished up 71% of the time (14 years observed). March is the weakest month (-2.1%). This is not a prediction: 14 years is a small sample, and the past is under no obligation to repeat.
Why does Biogen stock often rise in May?
May has averaged as its best month over 14 years (+2.8%, up 71% of years). No clearly established recurring seasonal driver explains this month — it's a statistical tendency over 14 years of history, not a prediction.
Is there a best month to invest in the stock market in general?
There's no universal rule: every stock has its own seasonality. For BIIB it's May (+2.8% on average over 14 years) — another stock will look completely different. The calendar effects people cite ("sell in May", the year-end rally) are market-wide averages, not laws: on BIIB, May is the most consistent month (71% positive years). We also rank all 12 months for the whole market.
Does stock seasonality actually work?
Careful. A month that rose 14 times out of 14 can simply be chance: with 12 months and a dozen years, patterns appear naturally even in random data. Seasonality describes what happened; it doesn't explain why and predicts nothing. Treat it as context, never as a standalone buy signal.
What data is this table based on?
On BIIB's real monthly closing prices from 2013 to 2026 (14 years), source Yahoo Finance. Each cell = the price change over that month. Price performance, excluding dividends. Incomplete months and quote gaps are excluded.