The takeaway
Tandem Diabetes Care Inc shows a pronounced seasonal pattern over 10 years of data — strongest in August (+17.9%) and softest in October (−9.3%).
Right now
In July, the stock has risen 50% of years, averaging +2.1% — essentially in line with the S&P 500.
The full picture
Tandem Diabetes Care Inc's most dependable month has been August, higher in 7 of 10 years; October has been its least reliable, up just 40% of the time.
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Month by month
The stock's clearest edge over the S&P 500 lands in August (+17.6 pts); it has trailed the market most in October (−10.3 pts).
“vs S&P” is Tandem Diabetes Care Inc’s average for a month minus the S&P 500’s average for that same month — isolating Tandem Diabetes Care Inc’s own seasonal edge from broad market drift.
Reality check
Over the last 5 years, August has closed higher 40% of the time versus 70% across the last 10 years — the pattern is weakening.
Figures are the typical (median) August 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
Strip the year back and a single month does the heavy lifting: August, up in 7 of 10 Augusts while the other eleven tend to blur together.
The headline flatters a touch — its +17.9% average sits well above the +9.3% a typical year delivers, the work of a few big Augusts. That reliability comes with real swings, mind — even August ranges by 40.4% from year to year, so any single year can land far from the average. Crucially, the gain is the stock's own rather than a rising tide's: August has cleared the S&P 500 by +17.6 points above the index. That consistency sets it apart from the field, where the average stock manages August only about 52% of the time.
Only April comes anywhere near it for reliability. At the other end of the calendar, October has been the soft spot — the weakest of 4 months that average a loss (−9.3%), and the edge isn't year-round — the stock has trailed the S&P 500 in October, November, and September. Its roughest month on record was a −67.1% October in 2017 — a reminder of how hard even a seasonal name can fall.
The pattern has softened of late, August's last five years slipping below its longer-run record.
The takeaway is less about when to buy than what to expect: August aside, the stock's months offer little reliable tilt. With returns that swing hard year to year, the signal is best held loosely.
Short answers on the stock's best month (August), its worst (October), and whether it really trades seasonally.
Yes, to a pronounced degree. Since 2016 its best month (August, +17.9%) has run well ahead of its worst (October, −9.3%) — the heatmap above shows how steady that gap has been year to year.
August has been the strongest, averaging +17.9% and closing higher in 7 of 10 years since 2016.
It's the weakest, averaging −9.3% — 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