IWM vs SPY: 0% overlap
iShares Russell 2000 ETF and SPDR S&P 500 ETF Trust share 0.0% of their portfolios by weight — computed as Σ min(wA, wB) over every holding both funds own.
You would hold two tickers and get the diversification of 2.0. Two funds that shared nothing would score 2.0; two identical funds score 1.0.
Top shared holdings
IWM and SPY hold 0 of the same securities. The ten contributing most to the overlap figure:
| Holding | in IWM | in SPY | Δ |
|---|
Where IWM and SPY differ
Sector weights as a share of each fund, ordered by the size of the gap rather than the size of the sector — two funds that overlap heavily still usually diverge somewhere.
| Sector | IWM | SPY | Δ |
|---|---|---|---|
| Information Technology | 12.8% | 37.5% | −24.7pp |
| Health Care | 19.9% | 9.1% | +10.7pp |
| Communication Services | 2.5% | 9.3% | −6.8pp |
| Financials | 19.0% | 12.4% | +6.7pp |
| Industrials | 14.7% | 8.9% | +5.8pp |
| Real Estate | 5.9% | 1.9% | +4.0pp |
| Energy | 6.1% | 3.4% | +2.7pp |
| Consumer Staples | 2.2% | 4.6% | −2.4pp |
Δ is IWM minus SPY, in percentage points. Sector data is not published by every issuer, so “Unclassified” is a real category rather than a gap in the table.
What each fund holds alone
100.0% of IWM by weight, held in no part of SPY.
99.9% of SPY by weight, held in no part of IWM.
A large count with a small weight is the usual shape: the positions one fund adds are typically its smallest ones.
Concentration and cost
| IWM | SPY | |
|---|---|---|
| Top 10 holdings | 3.3% | 36.9% |
| Positions held | 1,967 | 505 |
| Cost per $10,000 held, per year | $19 | $9 |
Cost is the expense ratio applied to $10,000; it excludes any brokerage commission, bid-ask spread or tax consequence. Figures are facts about the funds, not a suggestion about which to hold.
Frequently asked
How much do IWM and SPY overlap?
IWM and SPY overlap 0.0% by portfolio weight — largely distinct portfolios. They share 0 holdings. The figure comes from current issuer holdings files (IWM as of 2026-07-23, SPY as of 2026-07-23).
How is the overlap between IWM and SPY calculated?
As the sum of the smaller weight in each fund, over every holding both funds own: Σ min(wA, wB). If IWM holds a stock at 6% and SPY holds the same stock at 4%, 4% counts as shared. The result is bounded between 0% and 100%, and it is computed after looking through any fund-of-funds to the underlying holdings.
Is it redundant to hold both IWM and SPY?
That depends on your goals — we state facts, not advice. At 0.0% overlap, each fund still contributes meaningfully distinct exposure.
What does IWM own that SPY doesn't?
IWM holds 1,967 positions and SPY holds 505; 1,966 of IWM's positions don't appear in SPY at all, and they are 100.0% of IWM by weight.
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Related comparisons
Sources: issuer holdings files, IWM as of 2026-07-23, SPY as of 2026-07-23. Weights are fractions of each fund. Diagnostics, not advice.