🤝 BFF Take
XBI for Small-Cap Biotech Bets — IBB for Large-Cap Biotech Stability
XBI (SPDR S&P Biotech ETF) and IBB (iShares Biotechnology ETF) both target US biotech but with dramatically different approaches. XBI uses equal weighting across ~130 stocks — giving small clinical-stage biotechs the same weight as billion-dollar companies. This makes XBI much more volatile but also more sensitive to small-cap biotech catalyst events (FDA approvals, trial results). IBB is market-cap weighted, so Amgen, Gilead, and Regeneron dominate — giving it more large-cap stability. XBI costs 0.35%; IBB costs 0.44%. XBI is for traders and aggressive investors who want full biotech exposure including small-caps. IBB is for investors who want biotech exposure weighted toward established revenue-generating companies.
📋 Quick Takeaways
⚗️XBI equal-weights ~130 biotechs — small-cap clinical-stage companies get equal influence as large caps
🏢IBB market-cap weights — Amgen, Gilead, Regeneron dominate; more like large-cap pharma than pure biotech
💰XBI costs 0.35% vs IBB's 0.44% — XBI is also cheaper with broader small-cap exposure
📊 Data-Based Take: XBI has the lower fee
Whether the lower-cost fund suits your situation depends on your existing holdings, account type, tax situation, and how you use each fund. This is a cost comparison, not a personalized recommendation.
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Reviewed by a CFA® Charterholder · Data updated Jun 2026 · Educational only, not financial advice
IBB
iShares Biotechnology ETF
📋 XBI vs IBB — Key Facts Side by Side
| Metric |
XBI |
IBB |
| Fund Name |
SPDR S&P Biotech ETF |
iShares Biotechnology ETF |
| Issuer |
State Street |
iShares |
| Tracks Index |
S&P Biotechnology Select Industry |
NYSE Arca Biotechnology |
| Expense Ratio |
0.35% ✓ |
0.44% |
| Cost per $10K/yr |
$35.00 |
$44.00 |
| AUM |
$6B |
$8B |
| Holdings |
130 |
220 |
| Inception |
2006 |
2001 |
| 1-Year Return |
+4.20% |
+6.80% |
| 3-Year Return |
-8.40% |
-3.20% |
| 5-Year Return |
+1.80% |
+3.40% |
| Avg Bid-Ask Spread |
0.01% |
0.01% |
Data from ETF BFF database. Returns are annualised. Not investment advice.
📊 XBI vs IBB — Annualised Returns
Annualised returns (trailing, price-based). Past performance does not guarantee future results.
🎯 Should You Buy XBI or IBB?
Choose if...
XBI
- You want the lowest fees — saves ~$9/yr per $10K vs IBB
- You already use State Street and prefer staying within their fund family
Choose if...
IBB
- You want broader diversification (220 holdings vs 130)
- You already use iShares and prefer staying within their fund family
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❓ XBI vs IBB — Frequently Asked Questions
What is the main difference between XBI and IBB?
The key difference is weighting methodology. XBI uses equal weighting — every stock in the index gets roughly the same allocation. This means a tiny clinical-stage biotech with no revenue has the same weight as Amgen. IBB uses market-cap weighting — larger companies get larger allocations. This makes IBB behave more like a large-cap healthcare ETF, while XBI is a purer bet on the entire biotech ecosystem including small companies.
Which is more volatile — XBI or IBB?
XBI is consistently more volatile than IBB due to its equal-weight approach giving meaningful exposure to small-cap and clinical-stage biotechs. A single FDA approval or rejection in a small holding can cause XBI to spike or crash 2-5% in a day. IBB's large-cap dominance dampens individual stock impacts. In biotech bull markets, XBI typically outperforms; in biotech bear markets, XBI falls harder.
Is biotech a good long-term investment?
Biotech has been one of the most volatile sector ETFs over the past decade, with massive boom-bust cycles tied to drug approvals, clinical trial results, and interest rate sensitivity (biotech companies often burn cash and rely on capital markets). The long-term demographic and innovation tailwinds are real, but execution risk in individual companies is high. Both XBI and IBB have lagged the S&P 500 over most 5 and 10-year periods despite the compelling sector narrative.
Does IBB or XBI pay dividends?
Neither XBI nor IBB pays meaningful dividends. Biotech companies reinvest capital into R&D rather than distributions. Any dividend yield on these ETFs is incidental and very small. They are total-return vehicles driven almost entirely by price appreciation (or decline) rather than income.
What are the biggest holdings in XBI vs IBB?
In IBB, the top holdings are large-caps: Amgen, Gilead Sciences, Regeneron, Vertex Pharmaceuticals, and Moderna typically make up 30-40% of the fund. In XBI, no single stock exceeds 2-3% due to equal weighting — the top positions are often mid-cap or small-cap names that rotate frequently based on rebalancing. This makes XBI much harder to predict from a holdings perspective.
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ℹ️ Data shown is for educational purposes and may not reflect the most current figures. Returns are trailing price-based and exclude dividend reinvestment. Past performance does not guarantee future results. ETF BFF is not a licensed financial advisor — this is not personalized financial advice.