FXNAX vs MUB: 0% overlap
Fidelity U.S. Bond Index and iShares National Muni Bond ETF share 0.2% 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 — FXNAX 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
FXNAX and MUB hold 22 of the same securities. The ten contributing most to the overlap figure:
| Holding | in FXNAX | in MUB | Δ |
|---|---|---|---|
| 64990F | 0.0% | 1.5% | 1.4% |
| 73358X | 0.0% | 0.4% | 0.4% |
| 072024 | 0.0% | 0.4% | 0.4% |
| 235036 | 0.0% | 0.1% | 0.0% |
| 13063D | 0.0% | 2.7% | 2.7% |
| 02765U | 0.0% | 0.1% | 0.1% |
| 837151 | 0.0% | 0.4% | 0.4% |
| 235241 | 0.0% | 0.1% | 0.1% |
| 54438C | 0.0% | 0.3% | 0.3% |
| 73358W | 0.0% | 0.2% | 0.2% |
Where FXNAX and MUB 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 | FXNAX | MUB | Δ |
|---|---|---|---|
| Treasuries | 45.4% | 0.0% | +45.4pp |
| State Tax-Backed | 0.0% | 30.7% | −30.6pp |
| MBS Pass-Through | 16.5% | 0.0% | +16.5pp |
| Local Tax-Backed | 0.0% | 14.9% | −14.9pp |
| Utilities | 2.5% | 16.8% | −14.3pp |
| Corporate — industrial & other | 14.1% | 0.0% | +14.1pp |
| School Districts | 0.0% | 10.2% | −10.2pp |
| Transportation | 0.1% | 10.2% | −10.1pp |
Δ is FXNAX minus MUB, 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
99.7% of FXNAX by weight, held in no part of MUB.
91.0% of MUB by weight, held in no part of FXNAX.
A large count with a small weight is the usual shape: the positions one fund adds are typically its smallest ones.
Concentration and cost
| FXNAX | MUB | |
|---|---|---|
| Top 10 holdings | 69.4% | 17.2% |
| Positions held | 1,266 | 969 |
| Cost per $10,000 held, per year | $3 | $5 |
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 FXNAX and MUB overlap?
FXNAX and MUB overlap 0.2% by portfolio weight — largely distinct portfolios. They share 22 holdings. The figure comes from current issuer holdings files (FXNAX as of 2026-02-28, MUB as of 2026-07-23).
How is the overlap between FXNAX and MUB calculated?
As the sum of the smaller weight in each fund, over every holding both funds own: Σ min(wA, wB). If FXNAX holds a stock at 6% and MUB 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 FXNAX and MUB?
That depends on your goals — we state facts, not advice. At 0.2% overlap, each fund still contributes meaningfully distinct exposure.
What does FXNAX own that MUB doesn't?
FXNAX holds 1,266 positions and MUB holds 969; 1,244 of FXNAX's positions don't appear in MUB at all, and they are 99.7% of FXNAX by weight.
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Related comparisons
Sources: issuer holdings files, FXNAX as of 2026-02-28, MUB as of 2026-07-23. Weights are fractions of each fund. Diagnostics, not advice.