What Is MDY? SPDR S&P MidCap 400 ETF Trust

MDY is the SPDR S&P MidCap 400 ETF Trust, an exchange-traded fund from State Street Global Advisors. It tracks the S&P MidCap 400 Index, holding roughly 400 mid-sized US companies weighted by market value. Launched in 1995, it was one of the first mid-cap index funds and remains among the largest, giving investors broad exposure to the middle of the US stock market in a single trade.

MDY is issued by State Street Global Advisors under its SPDR brand, the same family behind the S&P 500 fund SPY. It tracks the S&P MidCap 400 Index, a benchmark of about 400 US companies that are too large to count as small caps but too small for the S&P 500. The Bank of New York Mellon serves as trustee for the trust structure.

Both MDY and iShares Core S&P Mid-Cap (IJH) track the same S&P MidCap 400 Index, so their holdings are nearly identical. The main difference is cost: MDY charges about 0.23% a year while IJH charges roughly 0.05%. MDY is also a unit investment trust, an older structure, whereas IJH is a modern open-end fund. For the same exposure, IJH is meaningfully cheaper.

MDY holds all 400 companies in the S&P MidCap 400 Index across every sector. Recent top positions include Twilio, Carpenter Technology, Illumina, Curtiss-Wright, TechnipFMC, ATI, Okta, nVent Electric, Flex, and XPO. Because the index is so diversified, no single stock is much above 1% of the fund, so returns are not driven by any one name.

MDY has an expense ratio of about 0.23% a year, which works out to roughly $23 on a $10,000 investment. That is low compared with active funds but high next to newer index funds tracking the same S&P MidCap 400 benchmark, such as IJH near 0.05% or SPMD near 0.03%. The higher fee reflects MDY's older unit investment trust structure.

Yes. MDY pays a dividend, typically distributed quarterly, made up of dividends passed through from its underlying mid-cap holdings. The yield is modest, recently around 1.0%, since mid-cap growth companies tend to reinvest more of their profits than pay them out. Because MDY is a unit investment trust, it holds dividends as cash until distribution rather than reinvesting them internally.

MDY trades like any stock, so you can buy it through Robinhood, Fidelity, Schwab, Public, or most other brokerages during market hours. Many brokers support fractional shares, so you can invest a set dollar amount rather than buying a whole share. If you use Walnut, you can connect your existing broker to track MDY inside a thematic basket alongside your other positions.

MDY manages roughly $26 billion in assets as of mid-2026, making it one of the larger mid-cap ETFs available. Its long track record since 1995 and deep trading volume mean tight bid-ask spreads and reliable liquidity, which matters for investors moving in and out of the fund. Size and age are part of why some investors stick with MDY despite cheaper alternatives.

MDY gives broad, low-cost exposure to US mid-cap stocks, a segment that has historically fallen between large caps and small caps in both risk and return. Whether it fits you depends on your goals, time horizon, and how much mid-cap exposure you already have. Walnut is not an investment adviser, and this is not a recommendation to buy or sell. Note that IJH tracks the same index for a lower fee.

MDY launched in May 1995, making it one of the oldest exchange-traded funds still trading and among the first to target mid-cap stocks. Its long history predates most rival mid-cap funds, and it helped establish the S&P MidCap 400 as a widely followed benchmark. That longevity gives it a track record spanning several full market cycles.

A mid-cap stock is a company whose total market value falls in the middle of the range, typically between roughly $3 billion and $20 billion, larger than small caps but smaller than the giants in the S&P 500. The S&P MidCap 400 that MDY tracks captures this group. Mid-caps are often seen as a blend of the growth potential of smaller firms and the stability of larger ones.

MDY and State Street's own SPMD both track the S&P MidCap 400, yet MDY charges about 0.23% versus roughly 0.03% for SPMD. The gap comes from structure and history: MDY is an older unit investment trust from 1995, while SPMD is a newer open-end fund built to compete on cost. Investors comfortable with the newer fund can get the same index far cheaper.

No. MDY holds only mid-cap companies in the S&P MidCap 400, so mega-cap names like Nvidia and Apple are not in the fund. Once a company grows large enough it typically graduates to the S&P 500 and leaves the mid-cap index. If you want exposure to the market's largest companies, you would pair MDY with an S&P 500 fund rather than expecting overlap.

IJR tracks the S&P SmallCap 600, holding smaller companies than MDY's S&P MidCap 400. Mid-caps in MDY are generally more established, with steadier earnings, while small caps in IJR carry higher potential volatility and growth. Some investors hold both to cover the full range below the S&P 500. The two indexes do not overlap, so combining them broadens diversification.

Put a few fields side by side: the expense ratio (fees compound over decades), the index or strategy it tracks, the top holdings and how much they overlap with what you already own, the dividend yield, and the AUM, liquidity, and bid-ask spread that affect trading costs. For index funds, tracking error (how closely it follows its index) and tax efficiency matter too. MDY's figures are above; the full method is in Walnut's guide on how to compare ETFs.