IBB vs MDY: Holdings Overlap
iShares · 254 holdings · $9.3B · as of 2026-03-31
MDYState Street® SPDR® S&P MIDCAP 400® ETF Trust
State Street (SPDR) · 399 holdings · $27.1B · as of 2026-08-06
Holdings snapshots are 128 days apart (IBB: 2026-03-31, MDY: 2026-08-06). Weights and index membership change between snapshots, so the true current overlap is typically higher than shown. For funds tracking the same index, the gap can be 5–15 points.
How similar are IBB and MDY?
iShares Biotechnology ETF (IBB, by iShares) holds 254 positions; State Street® SPDR® S&P MIDCAP 400® ETF Trust (MDY, by State Street (SPDR)) holds 399. They have 13 holdings in common, and by portfolio weight the two funds are 5.2% identical. In practical terms the pair is lightly overlapping, with most of each portfolio distinct.
- Overlap by Weight
- 5.2%Sum of the smaller weight of each shared holding
- Shared Holdings
- 13IBB holds 254 · MDY holds 399
- Weight in Shared Holdings
- IBB 13%·MDY 5%Share of each fund's weight in stocks both funds own
Based on each fund's latest official holdings. How is this calculated?
What makes each fund different
Only in IBB
241 of 254 positions (86.8% of the fund) are not held by MDY. Showing the top 30 by weight.
Sector Breakdown
| Sector | IBB | MDY |
|---|---|---|
| Health Care | 91.0% | 10.3% |
| Industrials | 0.0% | 25.9% |
| Financials | 0.0% | 16.0% |
| Information Technology | 0.0% | 15.6% |
| Consumer Discretionary | 0.0% | 11.6% |
| Other Sectors | 0.0% | 25.7% |
| Unclassified | 8.9% | 0.0% |
Share of each fund's portfolio weight by GICS-style sector, compiled from issuer fund data and our own classification of the holdings, not the issuers' published sector charts. “Unclassified” is weight we could not classify (9% of IBB, 0% of MDY).
Performance
| Fund | 1M | YTD | 1Y | 3Y (ann.) | 5Y (ann.) | 10Y (ann.) | Yield |
|---|---|---|---|---|---|---|---|
| IBB | -0.3% | +17.3% | +51.0% | +16.4% | +3.1% | +7.4% | 0.21% |
| MDY | +3.1% | +18.1% | +25.6% | +14.2% | +8.8% | +10.9% | 0.99% |
Total returns including dividends, from adjusted daily closes as of 2026-08-07. 3Y/5Y/10Y are annualized. Yield is trailing-12-month distributions over the last close. Past performance does not predict future results.
Project the growth of $10,000 in IBB vs MDY →
Shared Holdings(13)
The top 10 shared positions account for 88% of the overlap, led by ILMN, BMRN and UTHR.
 ILMNIllumina, Inc. | 1.68% | 0.80% | 0.80% |
|---|---|---|---|
 BMRNBioMarin Pharmaceutical, Inc. | 0.98% | 0.64% | 0.64% |
 UTHRUnited Therapeutics Corporation | 2.30% | 0.62% | 0.62% |
 NBIXNeurocrine Biosciences, Inc. | 1.18% | 0.44% | 0.44% |
 ROIVRoivant Sciences Ltd. | 1.24% | 0.43% | 0.43% |
 MEDPMedpace Holdings, Inc. | 1.00% | 0.36% | 0.36% |
 EXELExelixis, Inc. | 0.99% | 0.36% | 0.36% |
 ARWRArrowhead Pharmaceuticals, Inc. | 0.75% | 0.33% | 0.33% |
 CYTKCytokinetics Incorporated | 0.73% | 0.30% | 0.30% |
 HALOHalozyme Therapeutics, Inc. | 0.69% | 0.28% | 0.28% |
 KRYSKrystal Biotech, Inc. | 0.60% | 0.23% | 0.23% |
 RGENRepligen Corporation | 0.58% | 0.23% | 0.23% |
 BRKRBruker Corporation | 0.34% | 0.16% | 0.16% |
Frequently Asked Questions
How much do IBB and MDY overlap?
IBB and MDY overlap by 5.2% of portfolio weight. They share 13 holdings (IBB holds 254 positions and MDY holds 399), based on each fund's latest SEC-reported holdings.
Is it redundant to own both IBB and MDY?
The two portfolios are 5.2% identical by weight. Owning both is not redundant. Most of each portfolio is distinct, so the funds can serve different roles.
What are the biggest shared holdings of IBB and MDY?
The largest positions held by both funds are ILMN, BMRN, UTHR, NBIX and ROIV. Together the top 10 shared positions account for 88% of the total overlap.
What does IBB own that MDY doesn't?
241 positions (86.8% of IBB) are unique to IBB, led by GILD, AMGN and VRTX. In the other direction, 386 positions (99.9% of MDY) are unique to MDY.