The takeaway
Vanguard Short-Term Inflation-Protected Securities Index Fund ETF Shares shows a slight seasonal lean over 10 years of data — strongest in July (+0.5%) and softest in September (−0.2%).
Right now
In July, the fund has risen 80% of years, averaging +0.5%, roughly 1.7 pts behind the S&P 500.
The full picture
Vanguard Short-Term Inflation-Protected Securities Index Fund ETF Shares's most dependable month has been July, higher in 8 of 10 years; September has been its least reliable, up just 20% of the time.
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Month by month
The fund's clearest edge over the S&P 500 lands in January (+0.6 pts); it has trailed the market most in November (−2.1 pts).
“vs S&P” is Vanguard Short-Term Inflation-Protected Securities Index Fund ETF Shares’s average for a month minus the S&P 500’s average for that same month — isolating Vanguard Short-Term Inflation-Protected Securities Index Fund ETF Shares’s own seasonal edge from broad market drift.
Reality check
Over the last 5 years, July has closed higher 100% of the time versus 80% across the last 10 years — the pattern is strengthening.
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
Dependability is the through-line here. July stands out, higher in 8 of 10 Julys, but it heads a clutch of months that pull the year reliably upward.
Its average (+0.5%) and median (+0.4%) land within a hair of each other — the tell of steady, year-after-year gains rather than one outlier doing the work. That consistency sets it apart from the field, where the average stock manages July only about 61% of the time.
The lift is near-universal — strength runs through almost every month of the year, not one window. On the other side of the ledger, September is the year's quietest corner, essentially flat on average, and the edge isn't year-round — the fund has trailed the S&P 500 in November, July, and April.
July has now closed higher 7 years running. If anything it has sharpened recently — the last five Julys run ahead of the earlier years.
The takeaway is less about when to buy than what to expect: July aside, the fund's months offer little reliable tilt.
Short answers on the fund's best month (July), its worst (September), and whether it really trades seasonally.
Only mildly. The fund's months are fairly even — July is the firmest (+0.5%) and September the softest (−0.2%), a narrow spread that points to weak seasonality rather than a strong calendar effect.
July has been the strongest, averaging +0.5% and closing higher in 8 of 10 years since 2016.
It's the weakest, averaging −0.2% — 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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