The takeaway
iShares Prime Money Market ETF shows a slight seasonal lean over 1 years of data — strongest in October (+0.3%) and softest in November (+0.3%).
Right now
In July, the fund has risen 100% of years, averaging +0.3%, roughly 1.8 pts behind the S&P 500.
The full picture
iShares Prime Money Market ETF's most dependable month has been October, higher in 1 of 1 years; November has been its least reliable, up just 100% of the time.
| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Win rate % | — | |||||||||||
| Median return % | — | |||||||||||
| 2025 | — |
Month by month
The fund's clearest edge over the S&P 500 lands in February (+0.6 pts); it has trailed the market most in November (−2.1 pts).
“vs S&P” is iShares Prime Money Market ETF’s average for a month minus the S&P 500’s average for that same month — isolating iShares Prime Money Market ETF’s own seasonal edge from broad market drift.
Reality check
Not enough recent October history to say whether the pattern still holds.
Figures are the typical (median) October return and how often it rose — the last 1 years versus the last 1(the heatmap’s default window). This verdict stays anchored to that 1-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 October is the anchor — it has closed higher in all 1 Octobers, 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. No month is steadier: October's returns vary by just 0.0% year to year, and even its worst October in 1 years lost only 0.3% — the gentlest downside anywhere on its calendar. Few peers keep such company in October — the typical stock clears it just 53% 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: November 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 October, the sharper question is the rest of the year — outside its strong stretch, the calendar gives far less to lean on. With a short 1-year record, the signal is best held loosely.
Short answers on the fund's best month (October), its worst (November), and whether it really trades seasonally.
Only mildly. The fund's months are fairly even — October is the firmest (+0.3%) and November the softest (+0.3%), a narrow spread that points to weak seasonality rather than a strong calendar effect.
October has been the strongest, averaging +0.3% and closing higher in its one year on record since 2025.
It's the weakest month, but it has still averaged a small gain (+0.3%) — quiet rather than genuinely bad.
Explore
These names have the strongest July track records on record — a starting point for comparison.
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