Every month on IWM, against holding: six ahead on average, three after every check

Twelve fixed months on the small-cap ETF

IWM tracks the Russell 2000, an index of about two thousand smaller US companies. It is a widely held way to own US small caps as one position, which is why it stands in for them here. It is one fund: its results describe the index it tracks, not every small company, and not the small stocks of decades before it existed.

IWM began trading in May 2000, so January to May start in 2001 and the other months in 2000. Each December belongs to the year it starts in; the December 2025 trade ends in January 2026, after the 31 December 2025 research cutoff, so December's history ends in 2024. Each trade is compared with an ordinary IWM hold of exactly the same number of sessions.

The twelve months were fixed before any result was read: this page shows all of them, not a selection. SPY and QQQ are evaluated on the same twelve rules for context.

Six months ahead of holding, six behind

Each bar is one month's average lead over an ordinary IWM hold of the same length. A month can make money and still sit below the line: only January, February and September lost money on an average trade, and September by the most.

Three months pass every check; the rest lean on a few years or trail

An average can mislead, so each month is read against the same four checks: a positive average excess; still positive without its best year; ahead of holding in at least three years in five; and an average lead not small beside the ordinary hold itself (at least a quarter of it). Only May, November and December pass all of them, and May and December only just: May beat holding in 15 of 25 years and December beat holding in 16 of 25 years.

The other positive months depend on single years. April's average of +0.59 pp becomes −0.09 pp without 2009, and July's turns negative without 2022 too. June was ahead on average, +0.13 pp, but its median year trailed holding, −0.25 pp: a few large years carry it. October is the opposite case. It beat holding in 17 of 26 years, with a median year +1.47 pp ahead, yet averaged −0.04 pp, because its losses were large: 2008 alone trailed by 21.32 percentage points.

Twelve months tested together means twelve chances for one to look good by luck. No significance test or adjustment for those twelve tries is supplied with this evidence, so the readings describe history; they do not rank months as signals.

Small caps against the large-cap ETFs, on the same years

SPY and QQQ have longer histories, so for each month this table keeps only the years IWM has, and each ETF keeps its own matched benchmark. That changes which years are counted, not how any benchmark is computed.

The three ETFs agree on the sign in nine months: all ahead of holding in April, May, July and November, all behind in January, February, March, August and September. The months that differ are where small caps stand out, in either direction. In June and December IWM was ahead while QQQ trailed and SPY was level or behind. October went the other way: SPY and QQQ were well ahead and IWM was level. In July all three were ahead, the large-cap funds by more.

Three overlapping ETFs are not three independent tests: they share much of the same market move.

The year-end months, studied one by one

Three of these months have their own pages with every trade. November was IWM's strongest month here, and the November study on SPY compares the three ETFs on the same years. December was ahead on IWM, +0.83 pp, where on SPY it was close to level on the shared years; the December study sets out why. January, the month the small-cap January effect is named after, trailed holding by 0.99 pp on IWM; the January study tests that claim directly, against SPY and QQQ.

Every IWM month, open to inspection

All 306 monthly trades on IWM, as excess over each trade's matched hold. A dash is a month with no observation. The download holds every trade of all 36 rules on this page, with dates, gross returns and holds.

What this page cannot tell you

Each month has 25 or 26 observations, a short record for any one of them, and twelve of them read side by side invite picking the best after the fact. The excess is measured against an average of historical holds, so it is not a risk-adjusted return and not a hedged position. All figures are gross of costs.

Path risk is not measured. Open-to-open returns over a month do not show how far a month fell along the way. The cause of any pattern is not identified here. IWM is one fund tracking one index; it does not describe every small company, futures, leveraged funds or options.