Overlap · from SEC filings
IBB vs XBI: what actually overlaps
IBB and XBI: 41.57% of a dollar ends up in the same companies either way (SEC Form N-PORT, 2026-06-30), across 123 securities the two funds both hold. Every free comparison tool can list the tickers in common; this weights them, which is the part that decides whether owning both changes anything.
The short version
Held alone, IBB behaves like 34.6 equally weighted positions and XBI like 110.2. Held together in equal size they behave like 75.1 — less diversified than holding XBI on its own. The two funds hold 123 of the same securities, 41.57% of a dollar by weight, so the pair buys those companies twice.
Overlap here is the sum, over securities both funds hold, of the smaller of the two weights: the share of a dollar that sits in the same company either way. Matching is on CUSIP. Figures are as of each fund's own reporting date (2026-06-30 and 2026-06-30), which do not always align.
Not 50/50, or holding a third fund alongside these two? The portfolio calculator runs this same math for any weights, across up to 12 funds.
Side by side
as filed| IBB | XBI | |
|---|---|---|
| Assets | $10B | $11B |
| Holdings | 241 | 156 |
| Effective holdings | 34.6 | 110.2 |
| Top ten weight | 44.63% | 13.32% |
| Largest position | 8.06% | 1.49% |
| Priced at market (Level 1) | 100% | 99.9% |
| Reporting date | 2026-06-30 | 2026-06-30 |
Where the overlap actually is
123The ten shared positions that account for the most of it, with what each fund holds of its own. Shared is the lesser of the two — the part that is held in common either way. Where the two columns diverge, one fund is making a larger bet on that company than the other, and holding both does not average it away.
| Company | IBB | XBI | Shared |
|---|---|---|---|
| Moderna, Inc. | 1.979% | 1.412% | 1.412% |
| Revolution Medicines, Inc. | 2.773% | 1.205% | 1.205% |
| Natera, Inc. | 2.883% | 1.163% | 1.163% |
| Roivant Sciences Ltd. | 1.422% | 1.155% | 1.155% |
| Insmed, Inc. | 1.78% | 1.076% | 1.076% |
| Vertex Pharmaceuticals, Inc. | 8.06% | 1.057% | 1.057% |
| Biogen, Inc. | 2.46% | 1.032% | 1.032% |
| Ionis Pharmaceuticals, Inc. | 0.999% | 1.003% | 0.999% |
| Incyte Corp. | 1.745% | 0.998% | 0.998% |
| Amgen, Inc. | 7.808% | 0.995% | 0.995% |
What the difference is made of
24.47% · 14.22%24.47% of IBB sits in companies XBI does not hold at all, and 14.22% of XBI in companies IBB does not hold. The largest of each, by weight in its own fund:
- Argenx SE
- Illumina, Inc.
- BeOne Medicines Ltd.
- Ascendis Pharma A/S
- Genmab A/S
- Viking Therapeutics Inc
- SELLAS Life Sciences Group Inc
- Dianthus Therapeutics Inc
- Celcuity Inc
- TG Therapeutics Inc
By country of issuer
2026-06-30Where each fund's money sits by the issuer country its filer reported (incorporation, not revenue). Two funds can share companies and still differ here, and a pair that looks diversified by name can be one country twice.
| Country | IBB | XBI | Difference |
|---|---|---|---|
| United States | 84.47% | 94.86% | −10.39 |
| Netherlands° | 4.24% | 1.03% | +3.21 |
| Denmark | 2.40% | 0.00% | +2.40 |
| Switzerland | 2.16% | 1.02% | +1.14 |
| Bermuda° | 1.42% | 1.16% | +0.26 |
| Ireland° | 0.80% | 1.24% | −0.44 |
| Canada | 1.16% | 0.16% | +1.00 |
| Cayman Islands° | 0.86% | 0.00% | +0.86 |
| France | 0.68% | 0.00% | +0.68 |
| Germany | 0.66% | 0.00% | +0.66 |
What each fund did last quarter
Each fund's newest filing against its previous one. A pair whose overlap is rising or falling does so because of these moves; the figures are the same ones on each fund's page and in its feed.
Written about this pair
1This page is the measurement. These essays argue about what it means, with the figures as they stood when each was written.
Related comparisons
0Other pairs involving IBB or XBI, ordered by how much they overlap.
| Pair | Overlap | Combined effective |
|---|
Sources and limits
Computed from SEC Form N-PORT (NPORT-P), the portfolio report every registered US fund files. Positions below 0.001% of net assets are dropped; weights are normalised to each filing's own total.
Unit investment trusts including SPY and DIA do not file N-PORT, so no overlap can be computed for them. Where a comparison is missing from this site, that is usually why rather than an oversight.
Overlap says what is held in common, not what will move together. Two funds with no shared holdings can still fall together, and the effective holding count takes no account of correlation. All 275 pairs are in the concentration dataset, and every fund's own history is on its fund page.