MDY vs SPY: Correlation & Overlap
Measured on weekly returns over the past three years, SPDR S&P MidCap 400 ETF (MDY) and SPDR S&P 500 ETF Trust (SPY) carry a correlation of 0.80, a very strong link. The two funds also share 0% of their portfolios by weight.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are MDY and SPY?
Over the past 3 years, MDY and SPY moved with a correlation of 0.80, which is very strong, meaning they move nearly in lockstep. The link has loosened recently: the 1-year correlation (0.66) runs below the 3-year figure (0.80). Over 5 years the correlation is 0.86, and the annualized covariance of weekly returns is 191.0 %².
Among the 359 assets we track against MDY, SPY ranks #20 by 3-year correlation. Neither side won the trailing year by much: +18.3% against +20.6%. On a rolling one-year basis the correlation drifted between 0.64 and 0.91, a moderate band.
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.
MDY vs SPY: side by side
| MDY (SPDR S&P MidCap 400 ETF) | SPY (SPDR S&P 500 ETF Trust) | |
|---|---|---|
| 1-year return | +18.3% | +20.6% |
| 5-year return | +47.5% | +82.4% |
| Volatility (ann.) | 16.5% | 14.5% |
| Beta vs S&P 500 | 0.91 | 1.00 |
| Max drawdown (3Y) | -24.0% | -18.8% |
| Dividend yield | 1.02% | 1.01% |
| Expense ratio | 0.23% | 0.09% |
| Assets under management | $26.5B | $795.3B |
| Sector / category | ETF · US Small & Mid Cap | ETF · US Large Cap |
On the fund side, MDY sits in the Mid-Cap Blend category at State Street Investment Management, with $26.5B under management, 400 holdings, a 0.23% expense ratio, a 1.02% trailing dividend yield. SPY is a Large Blend fund from State Street Investment Management: $795.3B under management, 504 holdings, a 0.09% expense ratio, a 1.01% trailing dividend yield.
Portfolio overlap between MDY and SPY
The two portfolios are largely distinct, with 0 holdings in common adding up to 0% of fund weight. Where correlation shows the co-movement, the overlap shows its source.
Largest positions held only by MDY: TWLO (0.95%), P (0.94%), ILMN (0.93%), FTI (0.83%), ATI (0.80%). Only by SPY: NVDA (7.68%), AAPL (6.96%), MSFT (5.58%), AMZN (3.85%), GOOGL (3.03%).
Overlap = sum of the smaller of the two weights across common holdings, from issuer disclosures as of 2026-08-26.
Year-by-year returns
| Year | MDY | SPY |
|---|---|---|
| 2022 | -13.3% | -18.2% |
| 2023 | +16.1% | +26.2% |
| 2024 | +13.6% | +24.9% |
| 2025 | +7.2% | +17.7% |
| 2026 | +16.4% | +13.7% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are MDY and SPY good diversifiers for each other?
Not really. At 0.80, the two trade almost as one position, and owning both buys little extra protection.
FAQ
What is the correlation between MDY and SPY?
The MDY/SPY correlation stands at 0.80 on a 3-year window (1 year: 0.66, 5 years: 0.86), computed from weekly returns as of 2026-08-27.
Is SPY a good diversifier for MDY?
Not really. At 0.80, the two trade almost as one position, and owning both buys little extra protection.
How much do MDY and SPY overlap?
The two funds share 0 holdings amounting to 0% of weight, per issuer portfolio files dated 2026-08-26.
Use this data
$ curl https://www.pairbook.io/api/v1/pairs/mdy-vs-spy.json
Embed this badge (it refreshes with the data), with attribution:
[](https://www.pairbook.io/pair/mdy-vs-spy/)
Free with attribution; caching and terms are described in the API documentation.
Related comparisons
Hubs: MDY correlations · SPY correlations
