The takeaway
Vanguard Long-Term Treasury Index Fund ETF Shares shows a moderate seasonal pattern over 10 years of data — strongest in June (+1.6%) and softest in September (−1.9%).
Right now
In July, the fund has risen 60% of years, averaging +1.2%, roughly 1.0 pts behind the S&P 500.
The full picture
Vanguard Long-Term Treasury Index Fund ETF Shares's most dependable month has been June, higher in 8 of 10 years; September has been its least reliable, up just 20% of the time.
| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Win rate % | ||||||||||||
| Median return % | ||||||||||||
| 2025 | ||||||||||||
| 2024 | ||||||||||||
| 2023 | ||||||||||||
| 2022 | ||||||||||||
| 2021 | ||||||||||||
| 2020 | ||||||||||||
| 2019 | ||||||||||||
| 2018 | ||||||||||||
| 2017 | ||||||||||||
| 2016 |
Month by month
The fund's clearest edge over the S&P 500 lands in June (+1.3 pts); it has trailed the market most in October (−3.5 pts).
“vs S&P” is Vanguard Long-Term Treasury Index Fund ETF Shares’s average for a month minus the S&P 500’s average for that same month — isolating Vanguard Long-Term Treasury Index Fund ETF Shares’s own seasonal edge from broad market drift.
Reality check
Over the last 5 years, June has closed higher 60% of the time versus 80% across the last 10 years — the pattern is weakening.
Figures are the typical (median) June 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. June stands out, higher in 8 of 10 Junes, but it heads a clutch of months that pull the year reliably upward.
Its average (+1.6%) and median (+0.8%) land within a hair of each other — the tell of steady, year-after-year gains rather than one outlier doing the work. It is also the calendar's calmest month, its returns swinging least from year to year (a 2.1% spread), and even its worst June in 10 years lost only 1.2% — the gentlest downside anywhere on its calendar. Crucially, the gain is the fund's own rather than a rising tide's: June has cleared the S&P 500 by +1.3 points above the index. That consistency sets it apart from the field, where the average stock manages June only about 52% of the time.
A few other months pull their weight: March, July, and November have also closed higher more often than not. The weaker half of the year is plainer: September has been the soft spot — the weakest of 3 months that average a loss (−1.9%), and the edge isn't year-round — the fund has trailed the S&P 500 in October, April, and September.
The pattern has softened of late, June's last five years slipping below its longer-run record.
The takeaway is less about when to buy than what to expect: June aside, the fund's months offer little reliable tilt.
Short answers on the fund's best month (June), its worst (September), and whether it really trades seasonally.
Yes, to a moderate degree. Since 2016 its best month (June, +1.6%) has run well ahead of its worst (September, −1.9%) — the heatmap above shows how steady that gap has been year to year.
June has been the strongest, averaging +1.6% and closing higher in 8 of 10 years since 2016.
It's the weakest, averaging −1.9% — 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