What Is MDY? SPDR S&P MidCap 400 ETF Trust
Last updated August 2026
Short answer
MDY is the SPDR S&P MidCap 400 ETF Trust, one of the oldest ETFs, tracking the S&P MidCap 400 index of mid-sized US companies. It fills the gap between large-cap funds like the S&P 500 and small-cap funds, holding roughly 400 companies with market caps generally between a few billion and around $20 billion. At a 0.23% expense ratio it is pricier than newer mid-cap ETFs like IJH, which tracks the same index for a fraction of the fee.
MDY is issued by State Street SPDR and tracks S&P MidCap 400. It charges a 0.23% expense ratio, holds approximately $28.05B in assets under management, yields about 1.00%, and launched in May 1995.
What is MDY?
MDY is the SPDR S&P MidCap 400 ETF Trust, one of the oldest ETFs, tracking the S&P MidCap 400 index of mid-sized US companies. It fills the gap between large-cap funds like the S&P 500 and small-cap funds, holding roughly 400 companies with market caps generally between a few billion and around $20 billion. At a 0.23% expense ratio it is pricier than newer mid-cap ETFs like IJH, which tracks the same index for a fraction of the fee.
MDY is issued by State Street SPDR and tracks S&P MidCap 400, so a single ticker gives you the whole portfolio of underlying holdings weighted by the index's methodology rather than by any active stock-picking.
What does MDY hold?
MDY is weighted toward its largest constituents. As of July 2026, the top holdings are:
| Rank | Ticker | Company | % of MDY | |
|---|---|---|---|---|
| 1 | FLEX | Flex Ltd | 1.58% | |
| 2 | TWLO | Twilio Inc Class A | 0.82% | |
| 3 | FTI | TechnipFMC PLC | 0.79% | |
| 4 | CW | Curtiss-Wright Corp | 0.79% | |
| 5 | NVT | nVent Electric PLC | 0.77% | |
| 6 | STRL | Sterling Infrastructure Inc | 0.75% | |
| 7 | XPO | XPO Inc | 0.72% | |
| 8 | P | Everpure Inc Class A | 0.71% | |
| 9 | ILMN | Illumina Inc | 0.71% | |
| 10 | UTHR | United Therapeutics Corp | 0.68% |
The remaining holdings make up the balance of the fund, with weights tapering off below the top names. Because the index reconstitutes on a rolling basis, the roster stays current without active management. Each ticker above links to its individual stock guide in Walnut.
How do I invest in MDY?
There are three common ways to get MDY exposure. Buy shares (or fractional shares) of MDY directly at any major broker that lists it. Hold it as a core position and layer more concentrated ideas on top. Or build it into a thematic portfolio in Walnut, so MDY sits alongside other holdings that express the same thesis, with target weights you can rebalance toward. MDY trades like a stock during market hours, so you buy it the same way you would any listed share.
New to buying funds? See how to buy an ETF, step by step.
Is MDY a good buy?
Whether MDY is a good buy depends less on any single call and more on your time horizon and what you already hold: it tracks S&P MidCap 400, so the real question is whether you want that exposure in your mix and at what weight. We walk through valuation, concentration, and what would have to be true for it to outperform from here in is MDY a buy?
The bottom line on MDY
MDY gives you the S&P MidCap 400 in one ticker, a slice of the market that large-cap funds miss, but it charges 0.23% while iShares' IJH tracks the identical index at roughly 0.05%. MDY's advantages are its long history and options liquidity; for cost-focused buy-and-hold investors, IJH covers the same mid-cap exposure far more cheaply.
More on MDY
Whether MDY is worth buying today depends more on your time horizon and what you already hold than on any single call. We walk through valuation, concentration, and what would have to be true for it to outperform from here in is MDY a buy?
MDY yields 1.00% as of July 2026, paid by passing through the dividends of its underlying holdings. For the payout schedule, history, and how the distributions are taxed, see MDY dividend: yield and schedule.
New to funds like MDY? Start with what an ETF is, then how to buy an ETF, or browse the full guide to ETF investing.
Wondering how MDY fits the portfolio you already own? Walnut is an AI investing app that connects your brokerage read-only and answers questions like that about your actual holdings: overlap, concentration, and how each position tracks the S&P 500. Compare the best AI portfolio analyzers or see the best AI investing apps in 2026.
Investing in MDY with AI
Connect the broker you already use and ask Walnut's AI how MDY fits what you actually hold: what it overlaps with, what it leaves you exposed to, and how it has tracked the S&P 500. Read-only by default, and you approve anything before it reaches your broker.
FAQ
What is MDY?
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MDY is the SPDR S&P MidCap 400 ETF Trust, launched by State Street in May 1995. It tracks the S&P MidCap 400 index, giving investors exposure to mid-sized US companies that sit between the large-caps of the S&P 500 and the small-caps of the S&P SmallCap 600. It is one of the oldest ETFs in existence.
What is MDY's ticker symbol?
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MDY, listed on NYSE Arca. The full name is SPDR S&P MidCap 400 ETF Trust, issued by State Street Global Advisors. Like SPY, it is structured as a unit investment trust, one of the earliest ETF structures.
What is the S&P MidCap 400?
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The S&P MidCap 400 is an index of about 400 mid-sized US companies, generally with market capitalizations between roughly a few billion and about $20 billion. It captures companies that have grown beyond small-cap status but are not yet large-cap. Historically it has been a well-regarded gauge of the US mid-cap segment.
MDY vs IJH: which should I choose?
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Both track the identical S&P MidCap 400 index, so their holdings and returns are nearly the same before fees. The difference is cost: MDY charges 0.23% while iShares' IJH charges roughly 0.05%. For cost-focused long-term investors IJH is the cheaper choice; MDY's edge is its longer history and deeper options liquidity, which matters mainly to traders.
What is MDY's expense ratio?
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0.23% per year, or about $23 annually on a $10,000 position. That is reasonable in absolute terms but noticeably higher than newer mid-cap funds tracking the same index, which is the main reason cost-conscious investors often prefer IJH.
What is MDY's dividend yield?
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Approximately 1.0% as of July 2026, paid quarterly. Mid-cap companies as a group pay modest dividends, lower than many large-cap value stocks, because more of them reinvest earnings for growth. The yield varies with the underlying constituents' payout policies.
How do I buy MDY?
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MDY trades like a stock during US market hours through any broker, including Robinhood, Fidelity, Schwab, and Public. It is commission-free at major brokers and supports fractional shares at many of them. Investors often use it to add a mid-cap slice on top of a large-cap core position.
What is MDY's AUM?
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Approximately $28.05 billion as of July 2026, making it one of the larger mid-cap ETFs by assets, though the cheaper IJH has grown larger. MDY's assets reflect its long track record and continued use by traders who value its liquidity.
Why hold mid-cap stocks?
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Mid-cap companies can offer a blend of the growth potential of smaller firms and the relative stability of larger ones, and the mid-cap segment is often under-represented in portfolios built around large-cap index funds alone. Adding a mid-cap fund like MDY can fill that gap, though mid-caps carry more volatility than large-caps.
Does MDY overlap with the S&P 500?
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By design, no. The S&P MidCap 400 and the S&P 500 are constructed to be mutually exclusive, so a company in one is not in the other. This means MDY genuinely complements an S&P 500 fund rather than duplicating it, which is part of its appeal as a portfolio building block.
When was MDY created?
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May 4, 1995. It was one of the very first ETFs, following shortly after SPY, and helped extend the ETF concept beyond large-cap stocks into the mid-cap segment. Its long history is one reason it remains widely traded despite cheaper alternatives.
Is MDY a good investment?
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MDY provides diversified exposure to US mid-cap stocks, a segment that can enhance diversification beyond a large-cap core. Its main drawback is a higher fee than IJH for the same index. Walnut is not an investment adviser; whether MDY fits depends on your allocation goals and whether cost or liquidity matters more to you.
How is MDY different from a small-cap fund?
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MDY holds mid-sized companies from the S&P MidCap 400, while a small-cap fund like IJR (S&P SmallCap 600) holds smaller companies. Mid-caps are generally larger and somewhat less volatile than small-caps but still more volatile than large-caps. Some investors hold both to cover the full size spectrum below the S&P 500.
How do I compare MDY to similar ETFs?
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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.
Guides that feature MDY
MDY is one of the names covered in these guides. Each one puts the fund next to its peers so you can see where it fits rather than judging it alone.
Related ETFs
Walnut is informational, not investment advice. Holdings weights and fund statistics on this page are approximations stamped to July 2026; verify current figures against State Street SPDR's fund page or your broker before investing.