IWD vs MDY: 7% overlap
iShares Russell 1000 Value ETF and SPDR S&P MidCap 400 ETF Trust share 6.7% 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 1.9. Two funds that shared nothing would score 2.0; two identical funds score 1.0.
Top shared holdings
IWD and MDY hold 283 of the same securities. The ten contributing most to the overlap figure:
| Holding | in IWD | in MDY | Δ |
|---|---|---|---|
| ILMN | 0.1% | 0.8% | 0.7% |
| TWLO | 0.1% | 0.8% | 0.7% |
| OKTA | 0.1% | 0.6% | 0.6% |
| UTHR | 0.1% | 0.6% | 0.6% |
| MKSI | 0.1% | 0.6% | 0.6% |
| USFD | 0.1% | 0.6% | 0.5% |
| RBA | 0.1% | 0.6% | 0.5% |
| RS | 0.1% | 0.6% | 0.5% |
| SNX | 0.1% | 0.5% | 0.5% |
| FTI | 0.1% | 0.8% | 0.8% |
Where IWD 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 | IWD | MDY | Δ |
|---|---|---|---|
| Industrials | 11.3% | 25.4% | −14.1pp |
| Financials | 19.6% | 14.8% | +4.7pp |
| Consumer Staples | 7.4% | 3.1% | +4.3pp |
| Information Technology | 18.0% | 13.8% | +4.2pp |
| Real Estate | 3.7% | 6.9% | −3.2pp |
| Health Care | 12.7% | 9.7% | +3.1pp |
| Communication Services | 3.3% | 1.5% | +1.8pp |
| Materials | 3.7% | 5.4% | −1.8pp |
Δ is IWD 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
93.3% of IWD by weight, held in no part of MDY.
23.9% of MDY by weight, held in no part of IWD.
A large count with a small weight is the usual shape: the positions one fund adds are typically its smallest ones.
Concentration and cost
| IWD | MDY | |
|---|---|---|
| Top 10 holdings | 27.8% | 7.6% |
| Positions held | 872 | 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 IWD and MDY overlap?
IWD and MDY overlap 6.7% by portfolio weight — largely distinct portfolios. They share 283 holdings. The figure comes from current issuer holdings files (IWD as of 2026-07-23, MDY as of 2026-07-23).
How is the overlap between IWD and MDY calculated?
As the sum of the smaller weight in each fund, over every holding both funds own: Σ min(wA, wB). If IWD 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 IWD and MDY?
That depends on your goals — we state facts, not advice. At 6.7% overlap, each fund still contributes meaningfully distinct exposure.
What does IWD own that MDY doesn't?
IWD holds 872 positions and MDY holds 400; 588 of IWD's positions don't appear in MDY at all, and they are 93.3% of IWD by weight.
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Related comparisons
Sources: issuer holdings files, IWD as of 2026-07-23, MDY as of 2026-07-23. Weights are fractions of each fund. Diagnostics, not advice.