Key takeaway
– WART (also called weighted average maturity, WAM, in some contexts) measures the average remaining time to maturity of the assets in a fixed‑income pool (most commonly mortgage‑backed securities—MBS). It is a weighted average where each asset’s remaining term is weighted by its share of the pool’s outstanding principal.
– WART helps investors understand the pool’s timing risk and how that timing may change with prepayments, but it is not the same as duration or other measures of interest‑rate sensitivity.
– WART is simple to compute and useful for portfolio construction and disclosure, but it should be used together with cash‑flow and prepayment analysis to assess risk fully.
What WART shows (short)
– A single-number view of how long, on average, the principal in a security or portfolio remains outstanding.
– Larger WART → on average, money is tied up longer → greater potential sensitivity to changing interest rates and higher refinancing/extension risk.
– Smaller WART → cash returns sooner → less interest‑rate timing exposure (but higher reinvestment risk).
How WART is defined and calculated
Definition
– WART = sum over each loan/security i of (weight_i × remaining_term_i),
where weight_i = remaining_principal_i / total_remaining_principal, and remaining_term_i is expressed in consistent units (years or months).
Step‑by‑step practical calculation
1. Collect data for each asset in the pool:
• Remaining principal balance (outstanding).
• Remaining time to maturity (remaining months or years).
2. Compute the total remaining principal of the pool.
3. Compute each asset’s weight = remaining_principal_i / total_remaining_principal.
4. Multiply each asset’s weight by its remaining term to get the weighted remaining term.
5. Sum the weighted remaining terms across all assets to get the WART (in years or months as used).
Simple numeric example (walkthrough)
Pool: four mortgages with remaining principal and remaining maturity:
– Loan 1: $150,000 remaining, 5 years remaining
– Loan 2: $200,000 remaining, 7 years remaining
– Loan 3: $50,000 remaining, 10 years remaining
– Loan 4: $100,000 remaining, 20 years remaining
1. Total remaining principal = $150k + $200k + $50k + $100k = $500k.
2. Weights:
• Loan 1 weight = 150k / 500k = 0.30
• Loan 2 weight = 200k / 500k = 0.40
• Loan 3 weight = 50k / 500k = 0.10
• Loan 4 weight = 100k / 500k = 0.20
3. Weighted remaining terms:
• Loan 1: 0.30 × 5 = 1.5 years
• Loan 2: 0.40 × 7 = 2.8 years
• Loan 3: 0.10 × 10 = 1.0 year
• Loan 4: 0.20 × 20 = 4.0 years
4. WART = 1.5 + 2.8 + 1.0 + 4.0 = 9.3 years
Interpretation and uses
– The pool’s principal will be repaid, on average, in 9.3 years (ignoring prepayment variability). Investors can use this to compare across pools or to match asset/ liability horizons.
– WART is commonly disclosed in MBS and ABS offering documents and investor reports to summarize maturity profile.
WART and interest‑rate risk
– Longer WART generally implies greater sensitivity to interest‑rate changes because money is “locked in” longer—however:
• WART is a maturity/term metric, not a price‑sensitivity metric like duration or option‑adjusted spread (OAS). Two securities with the same WART can have different duration depending on coupon, cash‑flow timing, and embedded prepayment options.
• MBS have embedded prepayment optionality. When rates fall, prepayments rise and WART tends to shorten (contraction risk); when rates rise, prepayments fall and WART tends to lengthen (extension risk).
– For realistic interest‑rate risk assessment, combine WART with duration, cash‑flow modeling under different prepayment scenarios (e.g., CPR/PSA speeds), and option‑adjusted analysis.
WART vs. WALA (Weighted Average Loan Age)
– WALA measures the average age (time since origination) of loans in a pool, weighted by outstanding principal. It is a measure of how long loans have been outstanding.
– WART measures the average remaining time to maturity.
– Relationship: conceptually complementary—older loans (higher WALA) generally have less remaining term (lower WART), and younger loans (lower WALA) tend to have higher WART. In simple cases where loans shared a common original term, WALA + WART ≈ original weighted average term. But if original terms differ across loans, the relationship is more complex—so don’t treat WALA as a strict mathematical inverse of WART.
Prepayment risk (what it is and why it matters)
– Prepayment risk: borrowers repay principal earlier than scheduled (by refinancing or extra payments). For holders of MBS/ABS, prepayments alter the timing of cash flows and therefore change WART.
– Effects:
• Falling rates → borrowers refinance → prepayments rise → WART decreases (contraction). Investors receive principal earlier and must reinvest at lower rates (reinvestment risk).
• Rising rates → prepayments slow → WART increases (extension). Investors keep lower‑coupon cash longer while market yields rise (price falls).
– Prepayment models (e.g., PSA/CPR assumptions) are used to project WART under different interest‑rate paths.
Purpose of mortgage‑backed securities (MBS)
– MBS pool many individual mortgages and sell claims on the pooled cash flows to investors.
– Benefits:
• Diversification: single loan defaults are diluted across many mortgages.
• Liquidity and market access: investors can buy tradeable securities rather than direct whole loans.
• Funding and risk transfer: lenders convert loans to securities to raise capital and shift interest‑rate and credit risk.
– For investors, WART is one of the pool characteristics disclosed to summarize maturity timing.
WAM vs. WAL (briefly and practical difference)
– WAM (Weighted Average Maturity): average time to maturity weighted by principal; often used to describe maturity profile of pools or money market funds; WAM can account for interest‑rate resets in some contexts.
– WAL (Weighted Average Life): average time until principal is repaid (weighted by principal repayments over time). WAL often ignores interest‑rate resets and focuses on principal timing.
– In money market fund regulation, the SEC limits WAL to 120 days for certain funds. Check current regulator guidance for details.
– Key point: these are related but distinct measures—know which definition your issuer or fund uses.
Practical steps for investors — how to use WART
1. Calculate WART for candidate securities or obtain the issuer’s disclosed WART.
2. Run prepayment scenarios: compute WART under low, base, and high prepayment assumptions to understand how WART could change (and how quickly principal is returned).
3. Combine WART with duration and option‑adjusted valuation (OAS) to evaluate interest‑rate sensitivity and relative value.
4. Match liabilities: use WART as a rough input to match asset timing to liability needs (e.g., target a WART close to expected liability horizon).
5. Use hedging/portfolio strategies:
• Laddering: buy securities maturing across a range of dates to reduce reinvestment timing risk.
• Hedging: use interest‑rate swaps, futures, or options to manage duration and convexity.
• Tranche selection: choose senior or subordinated tranches of securitizations to change cash‑flow timing and credit exposure.
6. Monitor changes: track WART over time because it will change with prepayments and repayments; frequent monitoring helps detect changing risk profiles.
Limitations and cautions
– WART is a simple average and ignores intra‑period cash‑flow timing—doesn’t capture periodic principal paydowns or coupon flows.
– It does not directly measure price sensitivity; use duration/convexity for that purpose.
– In MBS, embedded options make cash flows path‑dependent—WART under one interest‑rate outcome can be very different under another.
– Always pair WART with detailed cash‑flow modeling and scenario testing.
Example of good practice (practical checklist)
– Obtain detailed pool data (original note amounts, remaining balances, remaining terms, coupon rates).
– Compute disclosed WART and WALA to understand age/remaining term.
– Run prepayment speed scenarios (e.g., 50%, 100%, 300% PSA or range of CPRs) and compute resulting WART and projected principal timing.
– Compute effective duration and OAS for those scenarios.
– Decide allocation or hedging based on combined view of WART, duration, credit risk, and market liquidity.
Further reading and sources
– Investopedia — Weighted Average Remaining Term (WART):
– Freddie Mac investor disclosures and MBS documentation:
– U.S. Securities and Exchange Commission — Money Market Fund Rules (for WAL/WAM guidance):
– Fidelity — Understanding Money Market and Bond Fund Terminology
Editor’s note: The following topics are reserved for upcoming updates and will be expanded with detailed examples and datasets.