ITOT vs MDY: 5% overlap
iShares Core S&P Total U.S. Stock Market ETF and SPDR S&P MidCap 400 ETF Trust share 5.0% of their portfolios by weight — computed as Σ min(wA, wB) over every holding both funds own.
You would hold two tickers and get the diversification of 2.0. Two funds that shared nothing would score 2.0; two identical funds score 1.0.
Top shared holdings
ITOT and MDY hold 399 of the same securities. The ten contributing most to the overlap figure:
| Holding | in ITOT | in MDY | Δ |
|---|---|---|---|
| FTI | 0.0% | 0.8% | 0.8% |
| ILMN | 0.0% | 0.8% | 0.8% |
| CRS | 0.0% | 0.8% | 0.8% |
| TWLO | 0.0% | 0.8% | 0.7% |
| CW | 0.0% | 0.8% | 0.7% |
| ATI | 0.0% | 0.8% | 0.7% |
| NVT | 0.0% | 0.7% | 0.7% |
| XPO | 0.0% | 0.7% | 0.7% |
| WWD | 0.0% | 0.7% | 0.6% |
| P | 0.0% | 0.7% | 0.6% |
Where ITOT and MDY differ
Sector weights as a share of each fund, ordered by the size of the gap rather than the size of the sector — two funds that overlap heavily still usually diverge somewhere.
| Sector | ITOT | MDY | Δ |
|---|---|---|---|
| Information Technology | 35.2% | 13.8% | +21.3pp |
| Industrials | 10.1% | 25.4% | −15.2pp |
| Communication Services | 8.7% | 1.5% | +7.2pp |
| Real Estate | 2.3% | 6.9% | −4.6pp |
| Materials | 2.1% | 5.4% | −3.3pp |
| Financials | 12.7% | 14.8% | −2.2pp |
| Consumer Discretionary | 8.8% | 10.2% | −1.4pp |
| Energy | 3.5% | 4.9% | −1.4pp |
Δ is ITOT minus MDY, in percentage points. Sector data is not published by every issuer, so “Unclassified” is a real category rather than a gap in the table.
What each fund holds alone
95.0% of ITOT by weight, held in no part of MDY.
0.0% of MDY by weight, held in no part of ITOT.
A large count with a small weight is the usual shape: the positions one fund adds are typically its smallest ones.
Concentration and cost
| ITOT | MDY | |
|---|---|---|
| Top 10 holdings | 32.7% | 7.6% |
| Positions held | 2,440 | 400 |
| Cost per $10,000 held, per year | $3 | $23 |
Cost is the expense ratio applied to $10,000; it excludes any brokerage commission, bid-ask spread or tax consequence. Figures are facts about the funds, not a suggestion about which to hold.
Frequently asked
How much do ITOT and MDY overlap?
ITOT and MDY overlap 5.0% by portfolio weight — largely distinct portfolios. They share 399 holdings. The figure comes from current issuer holdings files (ITOT as of 2026-07-23, MDY as of 2026-07-23).
How is the overlap between ITOT and MDY calculated?
As the sum of the smaller weight in each fund, over every holding both funds own: Σ min(wA, wB). If ITOT holds a stock at 6% and MDY holds the same stock at 4%, 4% counts as shared. The result is bounded between 0% and 100%, and it is computed after looking through any fund-of-funds to the underlying holdings.
Is it redundant to hold both ITOT and MDY?
That depends on your goals — we state facts, not advice. At 5.0% overlap, each fund still contributes meaningfully distinct exposure.
What does ITOT own that MDY doesn't?
ITOT holds 2,440 positions and MDY holds 400; 2,040 of ITOT's positions don't appear in MDY at all, and they are 95.0% of ITOT by weight.
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Related comparisons
Sources: issuer holdings files, ITOT as of 2026-07-23, MDY as of 2026-07-23. Weights are fractions of each fund. Diagnostics, not advice.