The takeaway
Inspire Medical Systems Inc shows a pronounced seasonal pattern over 8 years of data — strongest in January (+6.9%) and softest in March (−8.0%).
Right now
In July, the stock has risen 63% of years, averaging +3.8%, about +1.7 pts better than the S&P 500.
The full picture
Inspire Medical Systems Inc's most dependable month has been January, higher in 6 of 7 years; March has been its least reliable, up just 29% 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 November (+15.7 pts); it has trailed the market most in March (−9.0 pts).
“vs S&P” is Inspire Medical Systems Inc’s average for a month minus the S&P 500’s average for that same month — isolating Inspire Medical Systems Inc’s own seasonal edge from broad market drift.
Reality check
Over the last 5 years, January has closed higher 80% of the time versus 86% across the last 8 years — the pattern is holding.
Figures are the typical (median) January 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 — January. It has closed higher in 6 of 7 Januaries, a concentration the rest of the calendar can't touch.
Read it with one caveat: the average (+6.9%) runs well ahead of the median (+2.3%), so a handful of outsized years — not steady strength — do much of the lifting. That reliability comes with real swings, mind — even January ranges by 11.2% 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 — January has outpaced the S&P 500 by +7.1 points on average. Few peers keep such company in January — the typical stock clears it just 53% of the time.
It doesn't stand entirely alone — February, April, and June have leaned firm as well, if less emphatically. On the other side of the ledger, March has been the soft spot — the weakest of 4 months that average a loss (−8.0%), and the edge isn't year-round — the stock has trailed the S&P 500 in March, September, and October. Its roughest month on record was a −34.9% May in 2024 — a reminder of how hard even a seasonal name can fall.
Reassuringly, the tendency has held its shape: the recent five years still track the years behind them.
For a stock this dependable in January, 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 (January), its worst (March), and whether it really trades seasonally.
Yes, to a pronounced degree. Since 2018 its best month (January, +6.9%) has run well ahead of its worst (March, −8.0%) — the heatmap above shows how steady that gap has been year to year.
January has been the strongest, averaging +6.9% and closing higher in 6 of 7 years since 2018.
It's the weakest, averaging −8.0% — 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.
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