The takeaway
SPDR Series Trust - SPDR Bloomberg Barclays 3-12 Month T-Bill ETF shows a slight seasonal lean over 6 years of data — strongest in August (+0.3%) and softest in February (+0.2%).
Right now
In July, the fund has risen 80% of years, averaging +0.2%, roughly 1.9 pts behind the S&P 500.
The full picture
SPDR Series Trust - SPDR Bloomberg Barclays 3-12 Month T-Bill ETF's most dependable month has been August, higher in 4 of 5 years; February has been its least reliable, up just 60% of the time.
| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
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| Median return % | ||||||||||||
| 2025 | ||||||||||||
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| 2021 | ||||||||||||
| 2020 | — | — | — | — | — | — | — | — |
Month by month
Across the year the fund has stayed close to the S&P 500 — no single month stands out as a real edge.
“vs S&P” is SPDR Series Trust - SPDR Bloomberg Barclays 3-12 Month T-Bill ETF’s average for a month minus the S&P 500’s average for that same month — isolating SPDR Series Trust - SPDR Bloomberg Barclays 3-12 Month T-Bill ETF’s own seasonal edge from broad market drift.
Reality check
Over the last 5 years, August has closed higher 80% of the time versus 80% across the last 6 years — the pattern is holding.
Figures are the typical (median) August return and how often it rose — the last 5 years versus the last 6(the heatmap’s default window). This verdict stays anchored to that 6-year window even if you zoom the chart, so it never disagrees with the badges above.
In plain English
This is a fund you can almost set a calendar by, and August is the anchor — it has closed higher in 4 of 5 Augusts, the steadiest beat on its year.
The strength looks broad-based rather than freakish: its average (+0.3%) and median (+0.3%) sit close together, so no single blow-out year is flattering the figure. Set against the S&P 500, mind, August is close to a wash — the gain mirrors the market more than it beats it. Few peers keep such company in August — the typical stock clears it just 52% of the time.
The lift is near-universal — strength runs through almost every month of the year, not one window. The weaker half of the year is plainer: February 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.
For a fund this dependable in August, the sharper question is the rest of the year — outside its strong stretch, the calendar gives far less to lean on. With a short 6-year record, the signal is best held loosely.
Short answers on the fund's best month (August), its worst (February), and whether it really trades seasonally.
Only mildly. The fund's months are fairly even — August is the firmest (+0.3%) and February the softest (+0.2%), a narrow spread that points to weak seasonality rather than a strong calendar effect.
August has been the strongest, averaging +0.3% and closing higher in 4 of 5 years since 2020.
It's the weakest month, but it has still averaged a small gain (+0.2%) — quiet rather than genuinely bad.
Explore
These names have the strongest July track records on record — a starting point for comparison.
Before you trade