The takeaway
Biogen Inc shows a moderate seasonal pattern over 10 years of data — strongest in July (+2.3%) and softest in February (−3.8%).
Right now
In July, the stock has risen 60% of years, averaging +2.3% — essentially in line with the S&P 500.
The full picture
Biogen Inc's most dependable month has been July, higher in 6 of 10 years; February has been its least reliable, up just 20% of the time.
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Month by month
The stock's clearest edge over the S&P 500 lands in September (+2.0 pts); it has trailed the market most in March (−5.8 pts).
“vs S&P” is Biogen Inc’s average for a month minus the S&P 500’s average for that same month — isolating Biogen Inc’s own seasonal edge from broad market drift.
Reality check
Over the last 5 years, July has closed higher 20% of the time versus 60% across the last 10 years — the pattern is weakening.
Figures are the typical (median) July return and how often it rose — the last 5 years versus the last 10(the heatmap’s default window). This verdict stays anchored to that 10-year window even if you zoom the chart, so it never disagrees with the badges above.
In plain English
There's a real but measured seasonal tilt here, toward July — the firmest corner of the calendar, higher in 6 of 10 Julys.
The strength looks broad-based rather than freakish: its average (+2.3%) and median (+1.5%) sit close together, so no single blow-out year is flattering the figure. That reliability comes with real swings, mind — even July ranges by 8.0% from year to year, so any single year can land far from the average. Set against the S&P 500, mind, July is close to a wash — the gain mirrors the market more than it beats it. Some of that is a strong month market-wide, mind — July rises for about 61% of stocks — so the tendency is real if not unique.
July anchors a run, too: the July-through-September window has been the stock's reliable season. At the other end of the calendar, February has been the soft spot — the weakest of 4 months that average a loss (−3.8%), and the edge isn't year-round — the stock has trailed the S&P 500 in March, February, and October. Its roughest month on record was a −29.2% March in 2019 — a reminder of how hard even a seasonal name can fall.
The pattern has softened of late, July's last five years slipping below its longer-run record.
Treat it as a tendency rather than a rule — seasonality describes the past, not a promise.
Short answers on the stock's best month (July), its worst (February), and whether it really trades seasonally.
Yes, to a moderate degree. Since 2016 its best month (July, +2.3%) has run well ahead of its worst (February, −3.8%) — the heatmap above shows how steady that gap has been year to year.
July has been the strongest, averaging +2.3% and closing higher in 6 of 10 years since 2016.
It's the weakest, averaging −3.8% — historically a soft spot, though it still varies from year to year.
Explore
These names have the strongest July track records on record — a starting point for comparison.
Before you trade