FIBUX — Fidelity Flex U.S. Bond Index Fund
Data updated: 2026-07-24
FIBUX — Fidelity Flex U.S. Bond Index Fund. Long Total / Aggregate Bond · $4.03B AUM · 0.00% expense ratio. Holdings, fees, performance and SEC filings.
FIBUX Fund Overview
FIBUX — Fidelity Flex U.S. Bond Index Fund is a US mutual fund managed by Fidelity Salem Street Trust, categorised as Long Total / Aggregate Bond. ABC INVEST provides holdings, performance, costs, cashflows, risk data, prospectus documents and SEC filings, sourced from SEC filings.
- Type: US mutual fund
- Manager: Fidelity Salem Street Trust
- Category: Long Total / Aggregate Bond
- Assets under management: $4.03B
- 1-year return: 5.2%
- Ticker: FIBUX
- SEC CIK: 0000035315
- SEC series ID: S000056354
- Share class ID: C000177581
FIBUX Holdings
Top 10 holdings of Fidelity Flex U.S. Bond Index Fund by percentage of net assets, from the fund's latest SEC N-PORT filing.
| Holding | % of net assets |
|---|---|
| Fidelity Revere Street Trust | 1.66% |
| Ust Notes | 1.16% |
| Ust Notes | 0.95% |
| Ust Notes | 0.94% |
| Ust Notes | 0.89% |
| United States Treasury Bond | 0.82% |
| Ust Notes | 0.81% |
| Ust Notes | 0.81% |
| Ust Notes | 0.80% |
| United States Treasury Bond | 0.78% |
FIBUX Portfolio Allocation
Asset-class allocation of Fidelity Flex U.S. Bond Index Fund by percentage of net assets, from the latest SEC N-PORT filing.
| Asset class | Allocation |
|---|---|
| Fixed Income | 75.3% |
| Securitized | 25.8% |
| Cash & Equivalents | 1.7% |
FIBUX Performance
Total returns for FIBUX (as of 2026-09-01), from SEC filings.
| Period | Total return |
|---|---|
| YTD | 0.6% |
| 1 year | 5.2% |
| 3 years (annualised) | 4.0% |
| 5 years (annualised) | 0.2% |
FIBUX Risk Information
Risk metrics for FIBUX, derived from monthly returns in SEC filings.
- 1-year volatility (annualised): 3.4%
FIBUX Costs and Fees
FIBUX costs about $0 per $10,000 invested per year in fund expenses.
- Net expense ratio: 0.00%
- Gross expense ratio: 0.00%
- Portfolio turnover: 68%
- Brokerage commissions: 0.00 bps of average net assets (SEC N-CEN)
FIBUX Cashflows
Over the 12 months to 2026-05, Fidelity Flex U.S. Bond Index Fund had net inflows of $1.17B, from monthly SEC N-PORT filings.
| Month | Net flow |
|---|---|
| 2026-05 | $181.75M |
| 2026-04 | $98.40M |
| 2026-03 | $63.57M |
| 2026-02 | $109.38M |
| 2026-01 | $113.21M |
| 2025-12 | $95.23M |
FIBUX Debt Constituents
Largest debt holdings of Fidelity Flex U.S. Bond Index Fund by percentage of net assets, from the latest SEC N-PORT filing.
| Debt holding | % of net assets |
|---|---|
| Ust Notes | 1.16% |
| Ust Notes | 0.95% |
| Ust Notes | 0.94% |
| Ust Notes | 0.89% |
| United States Treasury Bond | 0.82% |
| Ust Notes | 0.81% |
| Ust Notes | 0.81% |
| Ust Notes | 0.80% |
| United States Treasury Bond | 0.78% |
| Ust Notes | 0.70% |
FIBUX Prospectus and SEC Filings
Official Fidelity Flex U.S. Bond Index Fund filings on SEC EDGAR — prospectus, portfolio holdings and annual reports.
- Prospectus (485BPOS) — filed 2025-10-27
- Prospectus (485BPOS) — filed 2024-10-25
- Prospectus (485BPOS) — filed 2023-10-25
- Portfolio holdings (N-PORT) — filed 2026-07-24
- Portfolio holdings (N-PORT) — filed 2026-04-24
- Portfolio holdings (N-PORT) — filed 2026-01-23
- Annual census (N-CEN) — filed 2025-11-12
- Annual census (N-CEN) — filed 2024-11-13
Related Funds
Other Long Total / Aggregate Bond funds tracked on ABC INVEST:
Data Sources
ABC INVEST compiles this page from public filings made to the U.S. Securities and Exchange Commission (SEC) through EDGAR: portfolio holdings and monthly cashflows from Form N-PORT, expenses and returns from fund prospectuses (Form 485BPOS) and the SEC DERA Risk/Return Summary data sets, annual data from Form N-CEN, and shareholder reports from Form N-CSR.