IWM vs SPY: how much do they really overlap?
IWM (iShares Russell 2000 ETF, tracking the Russell 2000) and SPY (SPDR S&P 500 ETF Trust, tracking the S&P 500) overlap by roughly 0% by weight. 0 of IWM's top 10 holdings also appear in SPY. A 50/50 blend of the two behaves like about 218 equally-weighted bets (diversification grade A). In short, the two funds hold almost none of the same securities — they are complementary, not redundant.
The same companies, in both funds
These 0 holdings appear in both IWM and SPY. The weight columns show how much of each fund each name represents.
| Holding | in IWM | in SPY |
|---|
Only in IWM
iShares Russell 2000 ETF — US small-cap. Its biggest holdings that SPY doesn’t have:
| MOGA MOOG INC CLASS A | 0.38% |
| HUT HUT CORP | 0.37% |
| VSAT VIASAT INC | 0.35% |
| BTSG BRIGHTSPRING HEALTH SERVICES INC | 0.35% |
| CYTK CYTOKINETICS INC | 0.35% |
| MXL MAXLINEAR INC | 0.34% |
| AGX ARGAN INC | 0.34% |
| UMBF UMB FINANCIAL CORP | 0.33% |
Only in SPY
SPDR S&P 500 ETF Trust — US large-cap. Its biggest holdings that IWM doesn’t have:
| NVDA NVIDIA Corporation | 7.38% |
| AAPL Apple Inc. | 6.47% |
| MSFT Microsoft Corporation | 4.28% |
| AMZN Amazon.com, Inc. | 3.68% |
| GOOGL Alphabet Inc. | 3.24% |
| AVGO Broadcom Inc. | 2.76% |
| GOOG Alphabet Inc. | 2.60% |
| MU Micron Technology, Inc. | 2.02% |
So — essentially different. Should you hold both?
IWM and SPY hold almost none of the same securities — they are complementary, not redundant. Held together they genuinely broaden your exposure — a 50/50 blend reaches ~218 effective positions (grade A), because they hold largely different securities.
Holdings as of — IWM: Jun 30, 2026 (iShares (BlackRock)); SPY: Jun 29, 2026 (State Street Global Advisors). Refreshed monthly. Overlap is measured across each fund’s largest holdings (top 50); the diffuse long tail barely moves the math.
See this for YOUR whole portfolio, free →IWM vs SPY — FAQ
- How much do IWM and SPY overlap?
- IWM and SPY overlap by approximately 0% measured by portfolio weight — that is the share of the smaller fund's holdings (by weight) that also sit inside the other. 0 of IWM's 10 largest holdings are also held by SPY. They share 0 of their listed top holdings in total.
- Is it redundant to hold both IWM and SPY?
- Because they hold almost none of the same securities — they are complementary, not redundant, holding both is not redundant — each fund covers largely different holdings, so together they broaden your exposure. A 50/50 blend has an effective 218 positions and a A diversification grade.
- What does SPY hold that IWM doesn't?
- SPY's largest holdings that IWM doesn't hold include NVDA, AAPL, MSFT, AMZN, GOOGL. Its category is US large-cap, versus IWM's US small-cap.
- Which is more concentrated, IWM or SPY?
- IWM's top 10 holdings are 26% of its listed weight; SPY's are 71%. The more concentrated fund leans harder on its largest names.