Weighted Average Maturity (WAM)

August 24, 2024 Fixed Income

Weighted average maturity measures a portfolio's average time to maturity, weighted by each holding's share of assets or principal.

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Weighted average maturity (WAM) measures the average maturity of a bond portfolio, fund, ladder, or cash-management pool after weighting each holding by its share of assets, principal, or market value. It gives a quick view of where the portfolio sits on the maturity spectrum.

WAM is most useful when the portfolio contains many securities. A single bond has a maturity date; a portfolio needs a weighted maturity summary.

Core Idea

The basic calculation is:

\text{WAM} = \sum_i w_i \times \text{Maturity}_i

Where $w_i$ is the holding’s portfolio weight and $\text{Maturity}_i$ is the relevant maturity measure for that holding.

SVG diagram showing three bond holdings weighted into a portfolio weighted average maturity.

A portfolio with more weight in long-dated bonds has a longer WAM. A portfolio concentrated in bills, notes, short corporates, or short municipals has a shorter WAM.

Worked Example: Portfolio WAM

Assume a $100,000 portfolio has three bullet bonds and uses current principal as the weighting basis:

Holding	Principal	Portfolio weight	Years to maturity	WAM contribution
Bond A	`$40,000`	`40%`	`1`	`0.40` years
Bond B	`$35,000`	`35%`	`3`	`1.05` years
Bond C	`$25,000`	`25%`	`7`	`1.75` years
Total	`$100,000`	`100%`	-	`3.20` years

\text{WAM} = (0.40 \times 1) + (0.35 \times 3) + (0.25 \times 7) = 3.20\text{ years}

The simple unweighted average is 3.67 years, but it is not the portfolio WAM because it treats the smaller seven-year holding as if it were the same size as the $40,000 one-year holding. Market-value weights could produce a different result, and regulated products may use prescribed maturity conventions.

Why It Matters

WAM matters because maturity profile affects liquidity, yield, rollover risk, reinvestment risk, and interest-rate sensitivity.

It helps investors and risk teams evaluate:

whether a bond ladder is short, intermediate, or long
whether a cash-management portfolio is staying inside maturity limits
whether a bond fund is extending maturity to reach for yield
how a portfolio compares with its benchmark maturity profile
how quickly principal can be expected to recycle into new market rates
whether maturity exposure is consistent with a mandate or liquidity need

WAM is not a full risk model, but it is a useful first screen for portfolio term exposure.

WAM vs. WAL, Duration, and Average Maturity

Measure	What it summarizes	Best use	Main caution
WAM	Weighted maturity of portfolio holdings	Fund, ladder, and cash-management maturity profile	Convention can vary by product and regulation
Average Life or WAL	Weighted timing of principal repayment	Amortizing, mortgage-backed, and asset-backed structures	Depends on repayment assumptions
Duration	Price sensitivity to yield changes	Rate-risk measurement	Not a maturity measure
Final maturity	Last legal maturity date of one security	Bullet-bond legal maturity check	Not enough for portfolios or amortizing structures
Average maturity	Plain-language average of holdings’ maturity timing	Fund and investor education	Must check whether it is weighted and how it is calculated

In money market fund reporting, WAM and WAL can follow specific regulatory calculation conventions. Do not assume a fund’s WAM is calculated the same way as a simple bond-ladder spreadsheet.

Public Source Checks

Useful public references include:

SEC Money Market Fund WAL and WAM Statistics: SEC data visualization for money market fund weighted average life and weighted average maturity statistics.
SEC Money Market Fund Reform Q&A: Staff Q&A discussing disclosure of WAM and WAL with money market fund portfolio holdings information.
FINRA Bonds: Investor education defining average maturity and explaining why longer average lives tend to increase rate sensitivity.
MSRB Glossary of Municipal Securities Terms: Municipal-securities glossary that connects average life, weighted average life, and weighted average maturity terminology.

These sources support public terminology and disclosure context. A portfolio-specific WAM conclusion still requires holdings, weights, maturity inputs, and calculation conventions.

When WAM Misleads

WAM can mislead when:

one average hides a barbell portfolio with both very short and very long maturities
WAM is compared across funds that use different conventions
maturity is treated as rate risk even though duration and convexity are better sensitivity measures
average life, final maturity, reset date, and legal maturity are mixed together
callable, floating-rate, or amortizing instruments are not handled consistently
liquidity risk is ignored because WAM looks short
credit or spread risk drives performance more than maturity exposure

Use WAM as a maturity-profile screen. Pair it with duration, WAL, credit quality, liquidity, sector exposure, and actual holdings before making a portfolio conclusion.

Average Life: Weighted timing of principal repayment, often called WAL.
Duration: Rate-sensitivity measure that complements WAM.
Bond Ladder: Portfolio structure where WAM helps summarize maturity spacing.
Weighted Average Credit Rating: Another weighted portfolio summary measure.

FAQs

Is WAM the same as duration?

No. WAM summarizes maturity timing. Duration estimates price sensitivity to yield changes.

Why can a small long-term holding affect WAM so much?

Because WAM multiplies each holding’s weight by its maturity. A small allocation to a very long maturity can contribute a large share of the weighted average.

Is WAM the same as weighted average life?

Not always. The terms can overlap in some contexts, but WAL usually focuses on principal repayment timing while WAM often summarizes portfolio maturity exposure. Always check the calculation convention.

Bond Laddering