The takeaway
Sutro Biopharma shows a pronounced seasonal pattern over 8 years of data — strongest in August (+7.2%) and softest in September (−7.5%).
Right now
In July, the stock has risen 43% of years, averaging +6.0%, about +3.9 pts better than the S&P 500.
The full picture
Sutro Biopharma's most dependable month has been August, higher in 6 of 7 years; September has been its least reliable, up just 13% of the time.
| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
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| 2018 | — | — | — | — | — | — | — | — |
Month by month
The stock's clearest edge over the S&P 500 lands in December (+8.8 pts); it has trailed the market most in February (−12.2 pts).
“vs S&P” is Sutro Biopharma’s average for a month minus the S&P 500’s average for that same month — isolating Sutro Biopharma’s own seasonal edge from broad market drift.
Reality check
Over the last 5 years, August has closed higher 100% of the time versus 86% across the last 8 years — the pattern is strengthening.
Figures are the typical (median) August return and how often it rose — the last 5 years versus the last 8(the heatmap’s default window). This verdict stays anchored to that 8-year window even if you zoom the chart, so it never disagrees with the badges above.
In plain English
The seasonal story is really one month's story — August. It has closed higher in 6 of 7 Augusts, a concentration the rest of the calendar can't touch.
The strength looks broad-based rather than freakish: its average (+7.2%) and median (+6.7%) sit close together, so no single blow-out year is flattering the figure. That reliability comes with real swings, mind — even August ranges by 16.3% from year to year, so any single year can land far from the average. Better still, that strength is the stock's own and not just a buoyant market — August has outpaced the S&P 500 by +6.9 points on average. Few peers keep such company in August — the typical stock clears it just 52% of the time.
Only October comes anywhere near it for reliability. The weaker half of the year is plainer: September has been the soft spot — the weakest of 8 months that average a loss (−7.5%), and the edge isn't year-round — the stock has trailed the S&P 500 in February, November, and September. Its roughest month on record was a −54.7% March in 2025 — a reminder of how hard even a seasonal name can fall.
August has now closed higher 6 years running. If anything it has sharpened recently — the last five Augusts run ahead of the earlier years.
For a stock this dependable in August, the sharper question is the rest of the year — outside its strong stretch, the calendar gives far less to lean on. With a short 8-year record and returns that swing hard year to year, the signal is best held loosely.
Short answers on the stock's best month (August), its worst (September), and whether it really trades seasonally.
Yes, to a pronounced degree. Since 2018 its best month (August, +7.2%) has run well ahead of its worst (September, −7.5%) — the heatmap above shows how steady that gap has been year to year.
August has been the strongest, averaging +7.2% and closing higher in 6 of 7 years since 2018.
It's the weakest, averaging −7.5% — 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