Bond ETFs 101 — Duration, Real Yields, and How to Track Your Fixed-Income Sleeve Across Every Account

Duration: The Number That Tells You How Risky Your Bond Fund Actually Is

Duration is the weighted average time, in years, at which a bondholder receives the cash flows of a bond. For a bond ETF, it is the average duration across every holding. Most beginner explanations stop there, but the second use of duration is the one that matters for portfolio construction: it is also the approximate percentage price change you should expect for a 1% move in yields, in the opposite direction.

A fund with duration of 6 will move roughly 6% in price for every 1% change in underlying yields. A fund with duration of 25 will move roughly 25% in price for the same move. The mechanical rule is the same for every Treasury, every aggregate fund, and every corporate bond ETF. The only question is the magnitude.

SHY and BIL sit at the short end (duration under 2). IEF and GOVT sit in the belly of the curve (duration 5 to 7).TLT, EDV, and VGLT sit at the long end (duration 15 to 25). BND and AGG are blended — about 6 years of duration because they hold a mix of intermediate Treasuries, mortgages, and short corporates. Most investors do not know the duration of their own bond sleeve. That is a problem.

Real Yield: The Only Return Number That Actually Counts

Nominal yield is the coupon plus the price change, expressed as a percentage of price. Real yield is the nominal yield minus the expected inflation rate over the bond's lifetime. Real yield is what determines your purchasing-power return. The distinction matters when you are comparing a Treasury to a CD to a money-market fund to a TIPS allocation.

A Treasury yielding 4.5% with 2.5% expected inflation gives you roughly 2.0% real. That is a useful number to know. A nominal 4.5% yield with 4% inflation gives you 0.5% real, which is barely above cash and exposes you to real losses if inflation surprises to the upside. TIPS funds (TIP, SCHP) explicitly pay the real yield plus an inflation adjustment, while nominal Treasury funds leave the inflation math to you.

The practical exercise is to look at the SEC 30-day yield of every bond fund you own, subtract your assumption for inflation over the holding period, and see what your real return actually is. If the answer is below 1%, you have a duration problem, an inflation-expectations problem, or a fund-selection problem — and you cannot tell which without the calculation.

The Four Flavors of Bond ETF You Probably Already Own

Treasury funds hold US government debt directly: SHY, IEF, TLT, GOVT, VGLT. They have no credit risk. Their risk is purely duration. Yields are exempt from state and local income tax.

Aggregate funds blend Treasuries with mortgages and investment-grade corporates: BND, AGG, SPAB, USB. They pick up some credit spread and a small yield premium over pure Treasuries. The duration is moderate. Most “core bond” sleeves sit in this bucket.

Corporate funds hold investment-grade or high-yield corporates: LQD, VCIT, HYG, JNK. They add credit risk on top of duration risk. In a benign environment they earn a yield premium. In a credit selloff they can lose money independently of Treasury moves.

TIPS funds hold Treasury Inflation-Protected Securities: TIP, SCHP, VTIP. The principal adjusts with CPI, so your real return is locked in at purchase. They are the only bond fund category where the inflation math is built into the price.

Why You Probably Do Not Know Your Real Bond Allocation

The mechanical problem is structural. Most investors hold bond funds across three or four accounts: a 401(k), a Roth IRA at Schwab, an aggregate ETF in a Fidelity brokerage, and a money-market sweep in Robinhood. None of those apps share data with each other. The asset-allocation pie chart in your 401(k) portal ignores the taxable accounts entirely. The aggregate pie chart in your brokerage app ignores the 401(k) entirely.

A consolidated view looks like this once you sync every account:

Sizing Duration, Not Just Dollars

Once the consolidated view exists, the next question is duration-weighted exposure. A 25% allocation that is 80% SHY and 20% TLT has roughly 6 years of duration. A 25% allocation that is 20% SHY and 80% TLT has roughly 20 years of duration. Same dollar allocation, very different price risk.

The spreadsheet lets you multiply each fund's value by its duration, then divide by total fixed-income value, to get a duration-weighted figure for the whole sleeve. If that number surprises you, the right response is to either change the mix (rotate from TLT to IEF) or change the size (cut the bond sleeve from 25% to 15% and hold the rest in cash). Both moves are mechanical — they do not require a view on rate paths or policy.

The other mechanical lever is real yield per dollar of duration risk. A 4.5% nominal Treasury at 2.5% expected inflation gives 2% real. A 5.2% nominal high-yield corporate at 2.5% expected inflation gives 2.7% real but adds credit risk on top. The spreadsheet is the only place you can run that comparison across all four accounts at once.

The Bottom Line

Bond ETFs are not complicated once you know which numbers matter: duration and real yield. The complication is operational. Your bond sleeve is split across accounts that do not talk to each other, and the only honest way to know your aggregate exposure is to consolidate the holdings into one sheet, sum the values by ticker, and look at the duration-weighted picture that emerges. Everything else — yield curve shape, macro forecasts, geopolitical risk premium — is downstream of those two mechanical numbers.

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