ACWI vs MDY: Correlation & Overlap
How closely do iShares MSCI ACWI ETF (ACWI) and SPDR S&P MidCap 400 ETF (MDY) trade together? Their weekly returns over three years give a correlation of 0.83, which is very strong. Looking through to holdings, 1.2% of the two portfolios is the same by weight.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are ACWI and MDY?
On 3 years of weekly data the ACWI/MDY correlation comes out at 0.83, very strong, meaning they move nearly in lockstep. The relationship has been stable: the 1-year correlation (0.75) sits close to the 3-year figure. The 5-year figure is 0.88, and annualized covariance runs at 188.4 %².
Within ACWI's tracked universe of 119 assets, MDY comes in at #32 by 3-year correlation. Twelve-month performance is nearly a tie, at +22.7% for ACWI and +18.3% for MDY. The link looks structural: the rolling one-year correlation barely moved, holding between 0.74 and 0.90.
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.
ACWI vs MDY: side by side
| ACWI (iShares MSCI ACWI ETF) | MDY (SPDR S&P MidCap 400 ETF) | |
|---|---|---|
| 1-year return | +22.7% | +18.3% |
| 5-year return | +69.0% | +47.5% |
| Volatility (ann.) | 13.8% | 16.5% |
| Beta vs S&P 500 | 0.92 | 0.91 |
| Max drawdown (3Y) | -16.5% | -24.0% |
| Dividend yield | 1.44% | 1.02% |
| Expense ratio | 0.32% | 0.23% |
| Assets under management | $32.5B | $26.5B |
| Sector / category | ETF · Global | ETF · US Small & Mid Cap |
ACWI, iShares's Global Large-Stock Blend fund, carries $32.5B under management, 1590 holdings, a 0.32% expense ratio, a 1.44% 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 ACWI and MDY
The two portfolios are largely distinct, with 45 holdings in common adding up to 1.2% of fund weight. Where correlation shows the co-movement, the overlap shows its source.
| Common holding | Weight in ACWI | Weight in MDY |
|---|---|---|
| ALV | 0.19% | 0.23% |
| CFR | 0.12% | 0.28% |
| CSL | 0.08% | 0.40% |
| AAL | 0.06% | 0.25% |
| G | 0.04% | 0.16% |
| TWLO | 0.03% | 0.95% |
| ORA | 0.03% | 0.17% |
| ILMN | 0.03% | 0.93% |
| FTI | 0.03% | 0.83% |
| P | 0.03% | 0.94% |
| SN | 0.02% | 0.37% |
| TRU | 0.02% | 0.45% |
| BURL | 0.02% | 0.54% |
| VAL | 0.02% | 0.15% |
| XPO | 0.02% | 0.62% |
Largest positions held only by ACWI: NVDA (4.64%), AAPL (4.41%), MSFT (3.35%), AMZN (2.41%), GOOGL (1.91%). Only by MDY: ATI (0.80%), NVT (0.69%), CRS (0.66%), USFD (0.65%), THC (0.65%).
Overlap = sum of the smaller of the two weights across common holdings, from issuer disclosures as of 2026-08-26. Top 15 common positions shown.
Year-by-year returns
| Year | ACWI | MDY |
|---|---|---|
| 2022 | -18.4% | -13.3% |
| 2023 | +22.3% | +16.1% |
| 2024 | +17.4% | +13.6% |
| 2025 | +22.4% | +7.2% |
| 2026 | +14.9% | +16.4% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are ACWI and MDY good diversifiers for each other?
Not really. At 0.83, the two trade almost as one position, and owning both buys little extra protection.
FAQ
What is the correlation between ACWI and MDY?
Using weekly returns as of 2026-08-27: 0.83 over 3 years, with 0.75 over the last year and 0.88 over 5 years.
Is MDY a good diversifier for ACWI?
Not really. At 0.83, the two trade almost as one position, and owning both buys little extra protection.
How much do ACWI and MDY overlap?
The two funds share 45 holdings amounting to 1.2% of weight, per issuer portfolio files dated 2026-08-26.
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Related comparisons
Hubs: ACWI correlations · MDY correlations
