FXAIX vs MDY: 0% overlap
Fidelity 500 Index and SPDR S&P MidCap 400 ETF Trust share 0.0% of their portfolios by weight — computed as Σ min(wA, wB) over every holding both funds own.
Different holding dates. These holdings were published about 5 months apart — FXAIX as of 2026-02-28, the rest through 2026-07-23. Each fund is compared using its most recent file, so any trading in between shows up as a difference.
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
FXAIX and MDY hold 1 of the same securities. The ten contributing most to the overlap figure:
| Holding | in FXAIX | in MDY | Δ |
|---|---|---|---|
| MOH | 0.0% | 0.3% | 0.3% |
Where FXAIX 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 | FXAIX | MDY | Δ |
|---|---|---|---|
| Information Technology | 31.8% | 13.8% | +18.0pp |
| Industrials | 8.3% | 25.4% | −17.0pp |
| Communication Services | 10.5% | 1.5% | +9.0pp |
| Real Estate | 2.0% | 6.9% | −4.8pp |
| Materials | 1.5% | 5.4% | −4.0pp |
| Unclassified | 3.3% | 0.0% | +3.3pp |
| Financials | 12.0% | 14.8% | −2.8pp |
| Consumer Staples | 5.4% | 3.1% | +2.3pp |
Δ is FXAIX 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
100.1% of FXAIX by weight, held in no part of MDY.
98.6% of MDY by weight, held in no part of FXAIX.
A large count with a small weight is the usual shape: the positions one fund adds are typically its smallest ones.
Concentration and cost
| FXAIX | MDY | |
|---|---|---|
| Top 10 holdings | 36.4% | 7.6% |
| Positions held | 506 | 400 |
| Cost per $10,000 held, per year | $1 | $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 FXAIX and MDY overlap?
FXAIX and MDY overlap 0.0% by portfolio weight — largely distinct portfolios. They share 1 holdings. The figure comes from current issuer holdings files (FXAIX as of 2026-02-28, MDY as of 2026-07-23).
How is the overlap between FXAIX and MDY calculated?
As the sum of the smaller weight in each fund, over every holding both funds own: Σ min(wA, wB). If FXAIX 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 FXAIX and MDY?
That depends on your goals — we state facts, not advice. At 0.0% overlap, each fund still contributes meaningfully distinct exposure.
What does FXAIX own that MDY doesn't?
FXAIX holds 506 positions and MDY holds 400; 504 of FXAIX's positions don't appear in MDY at all, and they are 100.1% of FXAIX by weight.
You probably hold more than two funds
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Related comparisons
Sources: issuer holdings files, FXAIX as of 2026-02-28, MDY as of 2026-07-23. Weights are fractions of each fund. Diagnostics, not advice.