Title: Why Mortgage Bonds Are at Risk if Interest Rates Rise—and if They Fall Dek: There are fewer people sitting on ultracheap home loans than you might think Publication: The Wall Street Journal — Heard on the Street Author: Telis Demos Date: 2026-09-14 (article:published_time 2026-09-14T09:30:00Z) URL: https://www.wsj.com/finance/why-mortgage-bonds-are-at-risk-if-rates-riseand-if-they-fall-ff897dd5 Length: ~5 min read (written article — no timestamps) Note: Written article captured from Stephen's logged-in WSJ session via Claude-in-Chrome, so there are no (mm:ss) cues. This file is a DETAILED STRUCTURED DIGEST of the article — facts, figures, attributions and a few short quoted phrases — rather than the full verbatim body, because the piece is copyrighted Dow Jones material (same convention as wsj/archive/2026-sep-08). Read the original at the URL above. --- THE HOOK — the sub-3% mortgage is disappearing - Millions fewer Americans hold a sub-3% mortgage than a few years ago. A relief for frustrated home buyers; the article calls it an ominous sign for investors. - Pandemic borrowers locked in superlow rates, but "life has continued": first-time buyers still bought, older mortgages were paid off, people gave up cheap loans to move for family or work. THE DATA (Intercontinental Exchange / ICE) - Active primary U.S. mortgage loans with rates under 3%: nearly 15 million at end-2021; under 12 million as of July 2026. - Share of unpaid principal balance on mortgages at 5% or higher: ~10% at end-2022; more than 40% as of July 2026. ECONOMIC CONSEQUENCE - In 2022 many homeowners were shielded from surging rates by their locked-in loans. - Today, rising yields mean buyers who had to borrow at higher rates must wait longer to refinance into lower monthly payments. INVESTMENT CONSEQUENCE — the refinance option is back in play - A much bigger portion of the mortgage market is now eager to refinance if rates fall, and will be put off by rising rates — the crucial dynamic for mortgage-backed securities (MBS) investors. - Fixed-income investors burned by the rate surge could turn to government-backed mortgage bonds for extra yield while still avoiding credit risk. THE VEHICLES AND THE NUMBERS - iShares MBS ETF (MBB): holds bonds issued by government-sponsored enterprises such as Fannie Mae and Freddie Mac that pool individual home loans. Annualized return of 4.3% over the past three years — about 1.2 percentage points more than the iShares U.S. Treasury Bond ETF (GOVT), per FactSet. - Yield spread: ~5.8% for the AGNC ICE UMBS 30-Year Current Coupon Index vs just under 5% for the 10-year Treasury. One reason mortgage bonds yield more is early-prepayment (refinancing) risk. WHY THE RISK WAS DORMANT — AND WHY IT ISN'T NOW - While rates surged, prepayment risk was subdued: 2% or 3% mortgages were never going to refinance at 6% or 7%, and rates were in no danger of dropping below pandemic levels. - The market has now tilted toward mortgages at rates that could realistically refinance lower, so the risk of loans prepaying much faster OR much more slowly is again a major consideration. THE TWO-SIDED TRAP (negative convexity) - Fewer refinancings lengthen a mortgage bond's life; many refinancings shorten it. Investors who think they are locking in the yield for a set period can be disappointed either way. - Shorter life: the returned money must be reinvested at lower yields. - Longer life: the bond's price becomes even more sensitive to higher rates. - Harley Bassman (author of The Convexity Maven, creator of the MOVE index): mortgage bonds give more yield than Treasurys, but the trade-off is you lose more when rates rise and make less when rates fall. THE RATE BACKDROP - For now there seems little prospect of rates falling — Treasury bonds are under pressure and the Federal Reserve is poised to tighten. - But if long-term yields start coming down — perhaps after some cyclical downturn in the artificial-intelligence sector — mortgage-bond holders could be surprised by the pace of repayments. WHY SPEEDS COULD SURPRISE TO THE FAST SIDE - Walt Schmidt, mortgage strategist at FHN Financial: average loan balances have risen, today's borrowers have higher credit scores, and more loans are serviced by nonbank firms, which aim to refinance customers aggressively because they earn on volume. - FHN strategists (July note): the market is "very complacent" about the potential for faster prepayment speeds. - Technology: Morgan Stanley strategists considered AI speeding up the laborious refinancing process, which could lead investors who model past borrower behavior to misprice the refinancing option borrowers will be more inclined to exercise. CLOSE - A possible consolation for those who missed superlow mortgage rates is the chance to buy higher-yielding mortgage bonds — but nothing lasts forever; even 30-year mortgages often have much shorter lives. --- About the author: Telis Demos writes for Heard on the Street and co-hosts the WSJ's "Take on the Week" podcast, covering money and banking (big banks, Wall Street, private markets, crypto, insurance, mortgages, credit cards, fintech). Source material (c) 2026 Dow Jones & Company, Inc. Saved for personal study only.