The takeaway
Vanguard Core Bond ETF shows a slight seasonal lean over 3 years of data — strongest in September (+1.1%) and softest in October (−1.2%).
Right now
In July, the fund has risen 50% of years, averaging +1.4%, roughly 0.8 pts behind the S&P 500.
The full picture
Vanguard Core Bond ETF's most dependable month has been September, higher in 2 of 2 years; October has been its least reliable, up just 50% of the time.
| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Win rate % | ||||||||||||
| Median return % | ||||||||||||
| 2025 | ||||||||||||
| 2024 | ||||||||||||
| 2023 | — | — | — | — | — | — | — | — | — | — | — |
Month by month
The fund's clearest edge over the S&P 500 lands in September (+1.3 pts); it has trailed the market most in April (−2.4 pts).
“vs S&P” is Vanguard Core Bond ETF’s average for a month minus the S&P 500’s average for that same month — isolating Vanguard Core Bond ETF’s own seasonal edge from broad market drift.
Reality check
Not enough recent September history to say whether the pattern still holds.
Figures are the typical (median) September return and how often it rose — the last 2 years versus the last 3(the heatmap’s default window). This verdict stays anchored to that 3-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. September stands out, higher in all 2 Septembers, but it heads a clutch of months that pull the year reliably upward.
Its average (+1.1%) and median (+1.1%) land within a hair of each other — the tell of steady, year-after-year gains rather than one outlier doing the work. It is among its calmest months, too, its returns swinging least from year to year (a 0.3% spread), and even its worst September in 3 years lost only 0.8% — the gentlest downside anywhere on its calendar. Crucially, the gain is the fund's own rather than a rising tide's: September has cleared the S&P 500 by +1.3 points above the index. It bucks the broad tape, besides: September lifts just 39% of stocks across the market.
A few other months pull their weight: January, June, and August have also closed higher more often than not. At the other end of the calendar, October has been the soft spot — the weakest of 2 months that average a loss (−1.2%), and the edge isn't year-round — the fund has trailed the S&P 500 in April, October, and December.
The takeaway is less about when to buy than what to expect: September aside, the fund's months offer little reliable tilt. With a short 3-year record, the signal is best held loosely.
Short answers on the fund's best month (September), its worst (October), and whether it really trades seasonally.
Only mildly. The fund's months are fairly even — September is the firmest (+1.1%) and October the softest (−1.2%), a narrow spread that points to weak seasonality rather than a strong calendar effect.
September has been the strongest, averaging +1.1% and closing higher in all 2 years on record since 2023.
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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