Why Your Bond ETF Lost Money: Duration, Explained Properly
August 19, 2026 · 2 min read · by ETFWinner Research
Bonds were supposed to be the safe part. Then they fell. The explanation is one number that most fund pages bury — and it predicts almost everything.
Nothing damages confidence in a portfolio faster than the defensive holding falling alongside the risky one. Investors who bought bond funds for stability and then watched them decline usually conclude that bonds are broken. They are not. They did exactly what the arithmetic says they must.
The one number that explains it
Duration measures how sensitive a bond fund is to interest-rate changes. As a rough rule, a fund with a duration of 17 years will lose about 17% of its value if comparable yields rise by one percentage point — and gain roughly as much if yields fall by the same amount.
This is not a risk that occasionally shows up. It is a mechanical relationship: existing bonds paying old, lower coupons must fall in price until their yield matches what new bonds offer. The longer the remaining life of those bonds, the more the price must move to close the gap.
Short, intermediate and long — three different products
SGOV and SHY sit at the short end, where price barely moves and the yield is essentially what you earn. BND and AGG are intermediate, blending government and corporate bonds across maturities. TLT holds long-dated Treasuries and is the most rate-sensitive of the group — the fund people buy for safety and are then shocked by.
They share the word "bond" and almost nothing else in terms of behaviour. Choosing between them is choosing how much interest-rate risk you want, and that decision matters far more than the fee.
| Ticker | Fund | Expense | YTD | Yield | AUM |
|---|---|---|---|---|---|
| SGOV | iShares 0-3 Month Treasury Bond ETF | 0.07% | — | — | $30B |
| SHY | iShares 1-3 Year Treasury Bond ETF | 0.15% | — | 4.10% | $25B |
| BND | Vanguard Total Bond Market ETF | 0.03% | 2.15% | 4.25% | $110B |
| AGG | iShares Core U.S. Aggregate Bond ETF | 0.03% | 3.20% | 4.35% | $100B |
| TLT | iShares 20+ Year Treasury Bond ETF | 0.15% | 2.50% | 4.15% | $45B |
What long bonds are actually for
Long-duration funds are not a stability holding. They are a bet that yields will fall — which typically happens in a recession, when central banks cut. That is precisely why they can work as a hedge against an equity crash driven by a growth shock.
They do not hedge inflation shocks. When inflation drives yields higher, long bonds and equities fall together, which is exactly the scenario that shattered the traditional balanced-portfolio assumption in recent years.
Choosing duration deliberately
- Money you need within two years: ultra-short or T-bill funds. Price risk is negligible.
- Core ballast in a long-term portfolio: intermediate aggregate funds. Enough yield to matter, enough duration to help in a recession, not enough to dominate the portfolio.
- An explicit recession hedge: long duration, sized small, and understood as a position with a view rather than a safety blanket.
ETFs mentioned in this guide
iShares 20+ Year Treasury Bond ETF
Vanguard Total Bond Market ETF
iShares Core U.S. Aggregate Bond ETF
iShares 1-3 Year Treasury Bond ETF
iShares 0-3 Month Treasury Bond ETF
Frequently asked questions
Why did my bond ETF go down when rates rose?
Existing bonds paying lower coupons must fall in price until their yield matches newly issued bonds. The longer the fund's duration, the larger that price fall.
What is duration in a bond ETF?
A measure of interest-rate sensitivity. Approximately, a fund loses its duration figure as a percentage for every one-point rise in comparable yields, and gains similarly when yields fall.
Is TLT safer than a savings account?
No. TLT holds long-dated Treasuries with no credit risk but very high interest-rate risk, so its price can swing sharply. A T-bill fund is far closer to cash.
Do bond ETFs ever mature?
Most do not. They continually roll their holdings to maintain a target maturity range, so unlike an individual bond there is no date at which you are guaranteed your principal back.