IBB vs MDY: Correlation & Overlap
Measured on weekly returns over the past three years, iShares Biotechnology ETF (IBB) and SPDR S&P MidCap 400 ETF (MDY) carry a correlation of 0.62, a strong link. By holdings, the two funds overlap 5.2% by weight.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are IBB and MDY?
Across a 3-year window, the weekly returns of IBB and MDY correlate at 0.62, strong. The link has loosened recently: the 1-year correlation (0.39) runs below the 3-year figure (0.62). Stretching to 5 years gives 0.62, with an annualized covariance of 212.9 %².
Among the 168 assets we track against IBB, MDY ranks #21 by 3-year correlation. Their recent paths diverged sharply: over the last 12 months IBB outperformed by 37.1 percentage points (+55.4% for IBB against +18.3% for MDY). The rolling one-year correlation moved between 0.48 and 0.81 over the past three years, a moderate range.
How is this computed?
Pearson correlation on weekly returns: ρ(A,B) = cov(rA, rB) / (σA · σB), over windows of 52, 156 and 260 weeks. Covariance is annualized (×52) and expressed in %². Full definitions on the methodology page.
IBB vs MDY: side by side
| IBB (iShares Biotechnology ETF) | MDY (SPDR S&P MidCap 400 ETF) | |
|---|---|---|
| 1-year return | +55.4% | +18.3% |
| 5-year return | +26.6% | +47.5% |
| Volatility (ann.) | 20.7% | 16.5% |
| Beta vs S&P 500 | 0.81 | 0.91 |
| Max drawdown (3Y) | -24.9% | -24.0% |
| Dividend yield | 0.22% | 1.02% |
| Expense ratio | 0.44% | 0.23% |
| Assets under management | $9.2B | $26.5B |
| Sector / category | ETF · Thematic | ETF · US Small & Mid Cap |
IBB is a Health fund from iShares: $9.2B under management, 235 holdings, a 0.44% expense ratio, a 0.22% trailing dividend yield. MDY, State Street Investment Management's Mid-Cap Blend fund, carries $26.5B under management, 400 holdings, a 0.23% expense ratio, a 1.02% trailing dividend yield.
Portfolio overlap between IBB and MDY
The two portfolios are largely distinct: 5.2% of the funds' weight sits in the same underlying holdings (13 common positions). Correlation tells you they move together; overlap tells you why.
| Common holding | Weight in IBB | Weight in MDY |
|---|---|---|
| ILMN | 2.34% | 0.93% |
| UTHR | 1.46% | 0.60% |
| ROIV | 1.31% | 0.45% |
| NBIX | 1.07% | 0.43% |
| EXEL | 0.94% | 0.39% |
| MEDP | 0.98% | 0.38% |
| HALO | 0.87% | 0.35% |
| BMRN | 0.86% | 0.35% |
| ARWR | 0.81% | 0.34% |
| CYTK | 0.65% | 0.29% |
| RGEN | 0.66% | 0.26% |
| KRYS | 0.64% | 0.26% |
| BRKR | 0.44% | 0.17% |
Largest positions held only by IBB: AMGN (8.43%), VRTX (7.89%), GILD (7.10%), REGN (5.68%), MRNA (3.76%). Only by MDY: TWLO (0.95%), P (0.94%), FTI (0.83%), ATI (0.80%), NVT (0.69%).
Overlap = sum of the smaller of the two weights across common holdings, from issuer disclosures as of 2026-08-26. Top 13 common positions shown.
Year-by-year returns
| Year | IBB | MDY |
|---|---|---|
| 2022 | -13.7% | -13.3% |
| 2023 | +3.8% | +16.1% |
| 2024 | -2.4% | +13.6% |
| 2025 | +28.0% | +7.2% |
| 2026 | +27.4% | +16.4% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are IBB and MDY good diversifiers for each other?
Somewhat, no more. With 0.62 correlation, most large moves hit both names, and the diversification benefit stays modest.
FAQ
What is the correlation between IBB and MDY?
Using weekly returns as of 2026-08-27: 0.62 over 3 years, with 0.39 over the last year and 0.62 over 5 years.
Is MDY a good diversifier for IBB?
Somewhat, no more. With 0.62 correlation, most large moves hit both names, and the diversification benefit stays modest.
How much do IBB and MDY overlap?
5.2% by weight, across 13 common holdings, based on issuer-disclosed portfolios as of 2026-08-26.
Use this data
$ curl https://www.pairbook.io/api/v1/pairs/ibb-vs-mdy.json
Embed this badge (it refreshes with the data), with attribution:
[](https://www.pairbook.io/pair/ibb-vs-mdy/)
Free with attribution; caching and terms are described in the API documentation.
Related comparisons
Hubs: IBB correlations · MDY correlations
