Thornburg's TMB bond ETF runs 1.4 years shorter duration than its index

As the third quarter's yield climb carried the 10-year Treasury to 5.26% and the 30-year to 5.59% — the highest since the financial crisis, according to Morningstar reporting carried by ETF Trends — it billed bond investors for duration in proportion to how much they held, with long-term Treasuries falling 7.65% while short-term core bonds lost 0.89%, a ratio of about eight and a half to one.

Sticky inflation and heavy corporate borrowing drove the climb, Sarah Hansen reported for Morningstar, with the Federal Reserve in September raising rates for the first time in more than three years and bond futures pricing better-than-even odds of two more hikes before year-end; since bond prices move opposite to yields, the climb came straight out of principal, and the longest maturities gave back the most.

Strategists cited by Morningstar point to the other side of the ledger, where higher yields mean more income and a thicker cushion against future price declines — the standard case for managing duration actively, and the quarter offers a clean read on what flexibility costs against what it earns.

Launched in February 2025, the Thornburg Multi Sector Bond ETF holds $260.98 million and charges 0.55%, paying monthly distributions with a 4.6% 30-day SEC yield as of August 31, according to Thornburg. Its managers invest across sectors, geographies, credit qualities and maturities, using Treasury futures and other assets to work through rate and credit cycles rather than track a fixed index, so as of August 31 its effective duration was 4.2 years against 5.6 for the Bloomberg U.S. Universal Index, with a yield to worst of 5.5% versus 5.1% for the benchmark.

One and four-tenths years shorter than the index works out to roughly a quarter less sensitivity to a parallel move in rates — the product a manager gets for declining to own the benchmark's maturity profile — and it is a live position with a cost, cutting the loss a rate rise inflicts while forgoing the gain a rate cut delivers. That means the two questions Dominic Pappalardo, chief multi-asset strategist for Morningstar Wealth, puts at the center of the outlook — how high rates go from here, and what will bring them back down — are questions a fund built to move its duration is designed not to have to answer in advance.

The fee is where the pitch gets harder to price, because 55 basis points exceeds the 40 basis points of yield-to-worst advantage TMB reported over the index, and an index yield is quoted before whatever an index fund charges to hold it, so the headline comparison overstates what an investor would collect.

Rate positioning is not the only dial: corporate bonds were 39% of TMB against 30.2% for the index, domestic Treasuries 18.9% against 39.5%, and asset-backed securities 14% against 0.4% — that last the widest relative departure at 35 times the index's weight — so a portfolio shaped that way will diverge from the benchmark on credit and securitized-spread calls at least as much as on rate calls, meaning the duration comparison describes only part of the 0.55%, and the fund's largest overweight sits in the sector whose borrowing Morningstar identifies as one of the forces lifting yields.

The wrapper is part of the story, too, because TMB launched in February 2025 into a stretch when new active bond ETFs have been arriving at a steady clip, and 55 basis points on $260.98 million comes to a little over $1.4 million a year — the revenue base out of which a duration call, a credit overweight and a 14% securitized sleeve all have to be paid for, whereas the indexed version of the same dollar buys the whole maturity profile at whatever the tracking fund charges.

The benchmark carried a 5.6-year duration and a 39.5% Treasury weight as of August 31, and a fund tracking it inherits both without anyone deciding to. Cheap beta is usually described as the absence of a position, but in a quarter that cost long Treasuries 7.65%, the position was a long maturity and a heavy government allocation, owned by default and paid for by fee. For advisors, "core" bond exposure says little about the rate risk inside it because the label carries no duration, and the quarter just ended shows what the difference between 4.2 and 5.6 years costs when yields jump.

This year's flows already voted on the default: a record $446 billion went into bond ETFs and landed at the front end, as this publication noted in September, where the quarter's damage stayed under a percentage point. The sequence inside the number was fast: our September 2 coverage put the 10-year at 4.78% with hike odds past two-thirds, and Morningstar's quarter-end figure of 5.26% is another 48 basis points of yield that front-end money sat through; a flat curve makes that parking cheap but it does not make it free.

Whether the active duration premium was worth paying is now a function of Pappalardo's second question: a 4.2-year portfolio beats a 5.6-year index while yields rise and trails it once they fall, and the two hikes futures markets give better-than-even odds to are the scenario TMB's positioning is built for. The fund's largest single position on October 1 was a U.S. Treasury at 10.14% of assets, inside a Treasury sleeve running at less than half the index's weight.