I've been a bit obsessed with trying to get a feel for exactly how much money bond funds might go down if and when interest rates start to rise. And now, thanks to the wonderful Jake Levy at BuzzFeed, I can show you, in animated, rubbable-GIF form!
Jake put together two GIFs for me. Both show what happens to a $1,000 bond fund over time: the first one shows the value of the fund at various different durations, and assumes that rates are rising at a modest 0.5% per year; the second one shows the effect of the speed with which rates rise, assuming a constant duration equal to that of the Barclays US Aggregate. If you view these charts at BuzzFeed, on a touch device, then you can click the little hand in the top right corner, drag your finger across them, back and forth, and see how things change.
These charts ultimately come out of a conversation I had with Emanuel Derman, and this clever tool from skewtosis. They're also purely about interest-rate risk, rather than credit risk: the duration points and initial yields for the first chart correspond to the figures for the 1-year, 2-year, 3-year, 5-year, 7-year, and 10-year Treasury bonds.
As for the lesson to be drawn from the charts, one interpretation is that the big risk to bond funds isn't rising rates so much as it's rapidly rising rates. Sure, if rates rise slowly and your fund has substantial duration, then you could lose a bit of money. But if rates rise quickly, you could lose a lot of money. In the BuzzFeed version of these charts, which you can see here, I say that in a rising interest rate environment, it's possible that bonds could actually be more risky than stocks. But I'm not sure what the implications are for asset allocation. Simon Lack, for one, would say that now's the time to pretty much get out of bonds entirely, given their large downside and small upside. But I remember that Larry Summers managed to lose a billion dollars using the argument that "rates can't fall any further."
So maybe the real lesson here is simply that there just isn't such a thing as a safe investment. Not even if it's a Treasury bond.