Portfolio Management Pathway · Liability-Driven and Index-Based Strategies

Fixed-Income Indexes and Index Construction for CFA Level III

Updated 8 October 2026 · Fact-checked

A fixed-income index measures the return of a defined set of bonds, usually weighted by market value. Bond indexes are hard to build and replicate because bonds mature, trade rarely and are issued in large numbers. In exam answers, link each index feature to the client's goal and to the cost of tracking it.

Understand Fixed-Income Indexes and Index Construction

A bond index is a rule-based list of bonds used to measure a market and to serve as a benchmark. Index providers set rules for which bonds enter: currency, issuer type, credit quality, minimum size and minimum remaining maturity. The index return is then the weighted return of its constituents.

Most broad bond indexes use market-value weighting. Each bond's weight is its market value outstanding divided by the total. This has a side effect that surprises many candidates: the more debt an issuer has, the larger its weight. Heavily indebted issuers, including governments and lower-quality borrowers, can dominate the index. This is issuer concentration in a perverse form, because the weights reward borrowing rather than strength.

Bond indexes differ from equity indexes in important ways. Bonds have a finite life, so constituents mature and drop out and the index must be rebalanced often. Index duration and other characteristics drift as bonds age and as new issues arrive. The universe is far larger than for equities, because one issuer can have many bonds. Most bonds trade over the counter, are illiquid and have wide bid-ask spreads, so prices may be matrix-based or dealer quotes rather than traded prices. Because of this, a full-replication fund is often costly or impossible.

This creates construction challenges. Which bonds are included and how they are priced both affect the reported return. Turnover is high from maturities, new issues, rating changes and bonds falling below size or maturity limits. Cash from coupons and redemptions must be reinvested, and the index assumes reinvestment without cost. Real investors face costs the index does not.

For benchmark selection, use the full checklist of qualities of a good benchmark. It should be:

unambiguous
investable
measurable
appropriate to the mandate
reflective of current investment opinions
specified in advance
accountable
owned by the manager

Match the benchmark's duration, credit quality and currency to the client's liabilities and objectives. A liability-driven client may prefer a custom benchmark that mirrors liability duration, because a broad market-value index may not fit.

Key rules to remember

Market-value weight of a bond: wᵢ = (Pᵢ × Parᵢ outstanding) ÷ Σ(Pⱼ × Parⱼ outstanding); Price should include accrued interest (full price) for market value. Larger debt means larger weight.
Index return: R_index = Σ wᵢ × Rᵢ; Weights are at the start of the period. Rᵢ is the total return of bond i (price change, coupon, accrued interest and reinvestment).
Index duration: D_index = Σ wᵢ × Dᵢ; Market-value-weighted average of constituent durations. Use it to compare the benchmark with liability duration.
Qualities of a good benchmark: Unambiguous, investable, measurable, appropriate, reflective of current investment opinions, specified in advance, accountable, owned; Use as a checklist when evaluating a proposed benchmark.

How to solve Fixed-Income Indexes and Index Construction questions

Use this method for any question on bond index features, construction problems or benchmark choice.

1Identify what the question asks: index type, a construction challenge, a benchmark choice or a calculation.
2Note the client's objective and constraints (liability duration, credit limits, currency, liquidity, cost sensitivity).
3List the index rules that matter: inclusion criteria, weighting method, pricing source and rebalancing frequency.
4For calculations, compute market values (price × par outstanding), then weights, then the weighted average return or duration. Show every step.
5Link the feature to its consequence: issuer concentration, duration drift, illiquidity, turnover or tracking cost.
6State a clear conclusion that answers the command word (identify, explain, recommend) and justify it in one or two sentences tied to the client.

Quickest way: Feature-to-consequence-to-client shortcut

When to use it: Use for item-set questions asking which statement about bond indexes is correct or which benchmark suits a client.

Spot the feature: market-value weighting, large universe, finite maturity or OTC pricing.
Recall its consequence: more debt gets more weight, high turnover, hard replication, stale or matrix prices.
Check the client's need: does the index duration and credit mix match the liabilities or mandate?
Eliminate options that treat bond indexes like equity indexes or ignore costs.
Pick the option that links the feature to the client's need.

Common mistakes in Fixed-Income Indexes and Index Construction

Treating market-value weighting as a sign of a high-quality or well-diversified index.
Equity market-cap weighting is seen as neutral, so candidates assume the same for bonds.
Fix: Remember that more borrowing means more weight. Say the index overweights the most indebted issuers and can concentrate in them.
Ignoring that bonds mature and the index must be rebalanced.
Equity indexes have no maturity, so candidates carry the idea over.
Fix: State that constituents drop out at maturity or when they fail rules, so turnover is high and duration drifts.
Assuming full replication is easy for bond indexes.
Equity index funds often hold every stock.
Fix: Note the huge number of securities, illiquidity and OTC trading. Replication is costly, so sampling is common.
Forgetting accrued interest when computing market value weights.
Candidates use the quoted price alone.
Fix: Use full price (clean price plus accrued interest) × par outstanding for market value.
Choosing a broad index for a client with specific liabilities without checking duration.
Candidates pick the best-known benchmark.
Fix: Compare index duration and credit mix with the client's liabilities and constraints. Propose a custom benchmark if they differ.

Worked examples

Example 1

An index holds three bonds. Bond A: full price 102, par outstanding ₹400 crore, return 2.0%. Bond B: full price 98, par outstanding ₹300 crore, return 3.0%. Bond C: full price 100, par outstanding ₹300 crore, return 1.0%. Calculate the weights and the index return.

Show the solution

Market value A = 1.02 × 400 = 408 crore.
Market value B = 0.98 × 300 = 294 crore.
Market value C = 1.00 × 300 = 300 crore.
Total = 408 + 294 + 300 = 1,002 crore.
Weights: A = 408 ÷ 1,002 = 0.4072; B = 294 ÷ 1,002 = 0.2934; C = 300 ÷ 1,002 = 0.2994.
Index return = 0.4072 × 2.0% + 0.2934 × 3.0% + 0.2994 × 1.0% = 0.8144% + 0.8802% + 0.2994% = 1.994%.

Answer: Weights are about 40.7%, 29.3% and 29.9%; the index return is about 1.99%.

Example 2

A pension fund with long-dated liabilities is offered a broad market-value-weighted government and corporate bond index as its benchmark. Explain two weaknesses of this benchmark for the fund and recommend a response.

Show the solution

Weakness 1: market-value weighting gives the largest weights to the most indebted issuers, so the fund's benchmark is concentrated in heavy borrowers rather than chosen for credit strength.
Weakness 2: the index duration reflects the market's maturity mix and drifts as bonds mature and new bonds are issued, so it may not match the long duration of the liabilities.
Link to the client: the fund's objective is to fund liabilities, so a benchmark with the wrong duration creates a mismatch that the index does not measure.
Recommendation: adopt a custom benchmark that matches liability duration and sets credit and issuer limits, and measure the manager against it.

Answer: The broad index overweights heavy borrowers and its duration may not match the liabilities. Recommend a custom, liability-matched benchmark with issuer and credit limits.

Exam tips

When asked why bond indexes differ from equity indexes, give at least three points: finite maturity, large universe with many bonds per issuer, illiquid OTC pricing and high turnover.
Always tie benchmark choice back to the client's liabilities, risk tolerance and constraints.
In calculations, use full price times par outstanding and show each weight so partial credit is secured.
Use the benchmark-quality checklist when asked to evaluate a benchmark, and name only the qualities that apply.
Answer exactly the number of points requested and use the command word: identify means list, explain means give reason.

Fixed-Income Indexes and Index Construction in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Fixed-Income Indexes and Index Construction: frequently asked questions

Why are bond indexes harder to replicate than equity indexes?

Bond indexes contain many securities, including many bonds per issuer, and most trade over the counter with wide spreads. Bonds also mature, so turnover is high. Full replication is therefore costly, and sampling is often used.

What is the main problem with market-value weighting in bond indexes?

The more debt an issuer has outstanding, the greater its weight. The index can become concentrated in the most indebted borrowers. This is why some investors prefer other weighting or custom benchmarks.

How do I choose a fixed-income benchmark?

Start with the client's objectives and liabilities. Then check the benchmark against the full list of qualities: unambiguous, investable, measurable, appropriate, reflective of current investment opinions, specified in advance, accountable and owned. Compare its duration, credit quality and currency with the mandate.

Why does index duration change over time?

Bonds age and mature, and new bonds are issued at different maturities. Both change the weighted average duration. Rebalancing and reinvestment rules also affect it.