Updated for the 2026-2027 CFA® Level I curriculum.
Fixed income indexes measure defined segments of the bond market. Their rules determine which securities are included and how much each security contributes to index performance.
Quick Answer
A fixed-income index is a rules-based measure of a selected bond universe. It may represent a broad market or a narrow segment defined by issuer, sector, maturity, credit quality, or currency. Eligibility, weighting, and rebalancing rules determine the exposure an index actually provides.
Key Takeaways
Broad indexes cover many eligible sectors; segment indexes focus on a narrower universe.
Eligibility rules can screen by size, maturity, rating, currency, or instrument type.
Market-value weighting gives larger debt issuers more index weight.
Rebalancing updates the universe as bonds are issued, mature, or lose eligibility.
The right benchmark should match the portfolio's mandate.
What You Need to Know for CFA Level I
Identify what a fixed income index represents.
Compare broad and narrow index coverage.
Explain how eligibility and weighting shape exposure.
Choose a benchmark whose scope matches the portfolio.
Index construction describes a benchmark. It is not the same as an active portfolio strategy.
What Is a Fixed-Income Index?
A fixed-income index tracks the return of a defined set of debt securities. The provider publishes rules for eligibility, valuation, weighting, and rebalancing. Investors use indexes to describe markets, compare performance, and guide passive portfolios.
Broad Market and Segment Indexes
A broad index and a segment index can report different returns because their eligible bonds differ. Compare the universe before using either as a benchmark.
Index type | Typical scope | Main use |
|---|---|---|
Broad aggregate | Multiple sectors and maturities | Measure a wide bond market |
Issuer or sector | Government, corporate, or securitized debt | Evaluate a focused allocation |
Maturity | Short, intermediate, or long term | Match an interest-rate exposure |
Credit quality | Investment grade or high yield | Match a credit mandate |
Currency or geography | Specified currency or market | Control regional or currency exposure |
How Eligibility and Weighting Shape Exposure
Eligibility rules define the universe. A bond may enter or leave as its remaining maturity, issue size, or credit rating changes. Rebalancing applies the rules on scheduled dates.
Many bond indexes use market-value weights:
where:
Index weight = the eligible issue's share of the index
Market value of eligible issue = current market value of the issue included in the index
Total market value of eligible issues = combined market value of all issues included in the index
This method often gives greater weight to entities with more eligible debt outstanding. A larger weight does not prove that the issuer is safer.
How to Choose the Right Index for a Comparison
Match the benchmark to the portfolio's eligible universe. A government-only portfolio should not be judged against a broad index containing corporate and securitized debt. Also compare maturity, currency, credit quality, and duration before deciding that a benchmark is appropriate.
Working Example
Index A includes only investment-grade government bonds in one currency. Index B includes government, corporate, and securitized debt across the same currency.
A government-only mandate is better matched to Index A because its eligible universe reflects the portfolio.
Index B may still describe the wider market, but its sector risk would make performance comparisons less precise.
Common Exam Traps
Assuming every bond index tracks the same universe
An index may limit inclusion by issuer, currency, credit quality, maturity, or sector. Read the eligibility rules before comparing returns or risks.
Ignoring how weighting changes exposure
A market-value-weighted index gives more weight to issuers with more eligible debt outstanding; it does not automatically favor the best credit quality.
Treating the largest index constituent as the safest bond
A large weight can reflect a large amount of debt issued. Credit risk still requires an assessment of the issuer and issue.
Confusing an index rule with an active manager's choice
A rules-based index applies its stated inclusion and weighting method; a portfolio manager can deliberately depart from those weights.
Practice Question
A market-value-weighted bond index is most likely to assign a larger weight to an issuer that:
has more eligible debt outstanding
has the highest coupon rate
has the fewest bonds outstanding
Correct Answer: Option A
A market-value-weighted bond index generally gives more weight to issuers with a larger market value of eligible debt outstanding.
Option B: A higher coupon rate does not by itself determine an issue’s market-value weight.
Option C: Having fewer bonds outstanding does not imply a larger market value and will often produce a smaller weight.
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FAQs About Types of Fixed-Income Indexes
What is a fixed income index?
It is a rules-based measure of the performance of a defined set of bonds.
What types of fixed-income indexes are common?
Broad, issuer, sector, maturity, credit-quality, currency, and geographic indexes are common.
Why can bond index weights favor larger debt issuers?
Market-value weighting assigns more weight to a larger amount of eligible debt outstanding.