The takeaway
OSI Systems Inc shows a moderate seasonal pattern over 10 years of data — strongest in May (+2.8%) and softest in September (−1.2%).
Right now
In July, the stock has risen 60% of years, averaging +2.1% — essentially in line with the S&P 500.
The full picture
OSI Systems Inc's most dependable month has been May, higher in 9 of 10 years; September has been its least reliable, up just 30% of the time.
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Month by month
The stock's clearest edge over the S&P 500 lands in November (+5.1 pts); it has trailed the market most in December (−3.6 pts).
“vs S&P” is OSI Systems Inc’s average for a month minus the S&P 500’s average for that same month — isolating OSI Systems Inc’s own seasonal edge from broad market drift.
Reality check
Over the last 5 years, May has closed higher 80% of the time versus 90% across the last 10 years — the pattern is holding.
Figures are the typical (median) May 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
This is a stock you can almost set a calendar by, and May is the anchor — it has closed higher in 9 of 10 Mays, the steadiest beat on its year.
A typical May brings +1.6%, a shade under the +2.8% average. No month is steadier: May's returns vary by just 3.3% year to year, and even its worst May in 10 years lost only 2.3% — the gentlest downside anywhere on its calendar. Better still, that strength is the stock's own and not just a buoyant market — May has outpaced the S&P 500 by +2.1 points on average. Few peers keep such company in May — the typical stock clears it just 55% of the time.
May anchors a run, too: the March-through-August window has been the stock's reliable season. On the other side of the ledger, September has been the soft spot — the weakest of 3 months that average a loss (−1.2%), and the edge isn't year-round — the stock has trailed the S&P 500 in December, October, and April. Its roughest month on record was a −36.5% January in 2016 — a reminder of how hard even a seasonal name can fall.
One run worth flagging just ended: a 9-year streak of positive Mays was snapped by a −2.3% close in 2025. Reassuringly, the tendency has held its shape: the recent five years still track the years behind them.
For a stock this dependable in May, the sharper question is the rest of the year — outside its strong stretch, the calendar gives far less to lean on.
Short answers on the stock's best month (May), its worst (September), and whether it really trades seasonally.
Yes, to a moderate degree. Since 2016 its best month (May, +2.8%) has run well ahead of its worst (September, −1.2%) — the heatmap above shows how steady that gap has been year to year.
May has been the strongest, averaging +2.8% and closing higher in 9 of 10 years since 2016.
It's the weakest, averaging −1.2% — 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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