Investing in the S&P MidCap 400: Mid-Cap ETFs and US Portfolio Guide
ETF Vehicles That Track This Index
Three ETFs track the S&P MidCap 400 Index, but they differ in structure, cost, and liquidity characteristics that matter depending on how you plan to use them.
IJH (iShares Core S&P Mid-Cap ETF) is the dominant choice for buy-and-hold investors. At a 0.05% expense ratio, it is one of the cheapest size-specific ETFs available. IJH is structured as an open-ended ETF, meaning it can reinvest dividends immediately and engage in securities lending, both of which help offset its already low costs further. Its asset base exceeds $60 billion, giving it high liquidity for large trades.
IVOO (Vanguard S&P Mid-Cap 400 ETF) charges 0.10% and provides the same index exposure through Vanguard's fund structure. It is a reasonable option for investors who prefer Vanguard accounts or want to hold mid-cap exposure alongside other Vanguard funds in a unified household.
MDY (SPDR S&P MidCap 400 ETF Trust) is the oldest of the three, launched in 1995, and charges 0.23%. Its legacy structure as a unit investment trust (similar to the original SPY) limits dividend reinvestment timing and prohibits securities lending. MDY has one meaningful advantage: a highly developed options market with significant open interest, which makes it the vehicle of choice for traders using mid-cap options strategies. For pure buy-and-hold investors, MDY's higher cost and structural limitations make it the weakest of the three choices.
Expense Ratios and Costs
The S&P MidCap 400's profitability requirement distinguishes it from competing mid-cap indexes, and its ETF vehicles are priced competitively for a size-specific segment fund.
| ETF | Index | Expense Ratio | Structure |
|---|---|---|---|
| IJH | S&P MidCap 400 | 0.05% | Open-end ETF |
| IVOO | S&P MidCap 400 | 0.10% | Open-end ETF |
| MDY | S&P MidCap 400 | 0.23% | Unit investment trust |
The 0.18% gap between IJH and MDY compounds meaningfully over long periods. On a $50,000 investment growing at 8% annually for 25 years, the difference in ending value is approximately $13,000, based purely on expense ratio drag. These figures are illustrative and assume no additional contributions.
The S&P MidCap 400's profitability screen (positive GAAP earnings required for inclusion) is not reflected in the expense ratio, but it is an embedded quality filter that affects the index's composition and historical return characteristics. Some investors treat this as a form of factor tilt toward profitability without paying a dedicated factor-fund premium. The three ETFs all deliver this quality filter as part of the base index, regardless of which you choose.
Portfolio Role and Benchmarking
Mid-cap stocks occupy a distinct risk and return profile between large-cap and small-cap equities. On a risk-adjusted basis, several multi-decade studies have found that mid-cap blend strategies outperformed both large-cap and small-cap strategies over long periods. The "mid-cap sweet spot" thesis holds that mid-cap companies have moved past the high-failure-rate startup phase but have not yet reached the slower-growth, more-efficient market pricing characteristic of large-caps.
The S&P MidCap 400 specifically has historically outperformed the Russell MidCap Index over many periods, an outcome widely attributed to the profitability screen. Because S&P requires earnings before admission, companies that would be included in a Russell mid-cap index purely on market capitalization but are losing money are excluded from the S&P 400. This quality tilt tends to reduce drawdown severity during market stress.
Investors typically add mid-cap exposure as a complement to a large-cap core position rather than as a standalone allocation. A common approach is to hold 10 to 20 percent of a domestic equity allocation in mid-caps via IJH, with the remainder in a large-cap fund like VOO or IVV. This reduces large-cap concentration without the higher volatility of a dedicated small-cap position. Investors with a single total-market fund (such as VTI) already have implicit mid-cap exposure at market weight; adding IJH overweights mid-caps above their natural market weight.
Financial planners who use asset class-based portfolio construction (rather than total-market approaches) often use the S&P MidCap 400 as their mid-cap benchmark, making IJH or MDY the relevant implementation vehicles for client portfolios built on that framework.
Tax Considerations for US Investors
The S&P MidCap 400 reconstitutes throughout the year as individual companies change rather than in a single annual batch. S&P adds replacement companies when a member is acquired, delisted, or no longer meets eligibility criteria. This ongoing reconstitution spreads trading activity over time, reducing the concentration of capital gain realization in any single period and generally keeping distributions lower than Russell mid-cap alternatives.
IJH and IVOO, as open-ended ETFs, benefit from the in-kind creation and redemption mechanism that allows capital gains to be distributed to exiting investors in the form of appreciated securities rather than cash. This keeps taxable capital gain distributions extremely low for remaining shareholders, making both ETFs suitable for taxable brokerage accounts.
MDY, as a unit investment trust, cannot use in-kind redemptions as flexibly, which has historically resulted in slightly larger capital gain distributions compared to open-ended ETF alternatives tracking the same index. For long-term investors in taxable accounts, this is a material consideration in favor of IJH or IVOO over MDY.
The S&P MidCap 400 typically carries a lower dividend yield than large-cap S&P indexes, partly because mid-cap companies often reinvest earnings rather than distributing them. Lower dividends reduce taxable ordinary income distributions for investors in taxable accounts, which is a modest tax advantage relative to high-dividend large-cap funds.
Tax-loss harvesting between IJH and IVOO is possible. Both track the same index and are issued by different fund families, which most brokerages treat as not substantially identical for wash-sale purposes. Switching from one to the other to realize a tax loss while maintaining continuous mid-cap exposure is a standard strategy, though investors should confirm the tax treatment with their own tax advisor.
Frequently Asked Questions
What is the S&P MidCap 400's eligibility requirement that differs from the Russell mid-cap indexes?
The S&P MidCap 400 requires companies to report positive earnings (as-reported GAAP earnings) over the most recent quarter and over the trailing four quarters combined. This profitability screen filters out loss-making companies that would otherwise qualify by size alone. In contrast, Russell mid-cap indexes include any company meeting the market-cap criteria regardless of profitability, which means the S&P MidCap 400 tends to be a higher-quality mid-cap index.
Is IJH or MDY better for long-term mid-cap investing?
For long-term buy-and-hold investors, IJH (0.05% ER) is typically the better choice over MDY (0.23% ER) because both track the same S&P MidCap 400 Index and IJH costs significantly less. MDY is a unit investment trust structure (similar to the original SPY), which limits its ability to reinvest dividends immediately and prevents securities lending. IJH, as an open-ended ETF, is more flexible and more cost-effective for most individual investors.
How does mid-cap allocation affect portfolio volatility?
Adding mid-cap exposure (5 to 20 percent of equity allocation) generally increases expected return relative to a pure large-cap portfolio while adding less volatility than a comparable small-cap allocation. Mid-cap stocks tend to have more established business models than small-caps, reducing single-stock business failure risk, while still participating in the growth premium associated with smaller companies.
References
- S&P Global: S&P MidCap 400 Index: Index methodology, eligibility criteria, and reconstitution rules for the S&P MidCap 400.