IWF vs MDY: 2% overlap
iShares Russell 1000 Growth ETF and SPDR S&P MidCap 400 ETF Trust share 2.2% 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
IWF and MDY hold 100 of the same securities. The ten contributing most to the overlap figure:
| Holding | in IWF | in MDY | Δ |
|---|---|---|---|
| CRS | 0.1% | 0.8% | 0.7% |
| ATI | 0.1% | 0.8% | 0.7% |
| WWD | 0.1% | 0.7% | 0.6% |
| XPO | 0.1% | 0.7% | 0.6% |
| MTZ | 0.1% | 0.6% | 0.5% |
| STRL | 0.1% | 0.6% | 0.5% |
| BURL | 0.1% | 0.6% | 0.5% |
| P | 0.1% | 0.7% | 0.6% |
| MTSI | 0.1% | 0.5% | 0.5% |
| LSCC | 0.1% | 0.5% | 0.5% |
Where IWF and MDY 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 | IWF | MDY | Δ |
|---|---|---|---|
| Information Technology | 55.0% | 13.8% | +41.1pp |
| Industrials | 8.5% | 25.4% | −16.8pp |
| Communication Services | 15.7% | 1.5% | +14.2pp |
| Financials | 4.7% | 14.8% | −10.1pp |
| Real Estate | 0.4% | 6.9% | −6.4pp |
| Materials | 0.3% | 5.4% | −5.2pp |
| Energy | 0.5% | 4.9% | −4.4pp |
| Health Care | 5.6% | 9.7% | −4.1pp |
Δ is IWF minus MDY, 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
97.8% of IWF by weight, held in no part of MDY.
66.1% of MDY by weight, held in no part of IWF.
A large count with a small weight is the usual shape: the positions one fund adds are typically its smallest ones.
Concentration and cost
| IWF | MDY | |
|---|---|---|
| Top 10 holdings | 56.1% | 7.6% |
| Positions held | 370 | 400 |
| Cost per $10,000 held, per year | $19 | $23 |
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 IWF and MDY overlap?
IWF and MDY overlap 2.2% by portfolio weight — largely distinct portfolios. They share 100 holdings. The figure comes from current issuer holdings files (IWF as of 2026-07-23, MDY as of 2026-07-23).
How is the overlap between IWF and MDY calculated?
As the sum of the smaller weight in each fund, over every holding both funds own: Σ min(wA, wB). If IWF holds a stock at 6% and MDY 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 IWF and MDY?
That depends on your goals — we state facts, not advice. At 2.2% overlap, each fund still contributes meaningfully distinct exposure.
What does IWF own that MDY doesn't?
IWF holds 370 positions and MDY holds 400; 269 of IWF's positions don't appear in MDY at all, and they are 97.8% of IWF by weight.
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Related comparisons
Sources: issuer holdings files, IWF as of 2026-07-23, MDY as of 2026-07-23. Weights are fractions of each fund. Diagnostics, not advice.