“Don’t multiply by two and expect to earn 12 percent for the year,” said Kathy Jones, chief fixed income strategist at the Schwab Center for Financial Research.

If, as expected, the Federal Reserve reduces its short-term interest rate later this year, Ms. Jones said, longer-term bond rates could rise slightly because the Fed’s move “will alleviate concerns about a recession.” That would cause longer-term bond prices to fall slightly — bond yields and prices move in opposite directions — damping fund and E.T.F. total returns.

Ms. Jones said the recent reversal in rates hurt the most cautious investors parked on the sidelines in cash and short-term bonds. Even someone who sought out a high-yielding online bank savings account, such as Goldman Sachs’s Marcus, earned an annual yield of only 2 percent or so, which is less than half what longer-term bonds delivered in the last six months. “Lots of clients were waiting and waiting to jump on something attractive, and missed out,” said Ms. Jones, who thinks we are now back to an interest rate outlook where interest rates — and thus the yields you earn on your bond investments — are going to be “lower for longer.”

Though the United States economy is showing signs of slower growth, Mr. Rieder says he thinks it is “in pretty good shape” compared with most other parts of the world. Japan and the European Central Bank are contemplating further stimulus for their struggling economies.

Low as United States yields may be, Japanese government bonds have a negative yield — meaning they will lose value if investors hold them to maturity — and in the eurozone, sovereign debt yields less than 1 percent.

“The risk is a global recession, and that is where the Fed is going to be pre-emptive and consider reducing rates,” Mr. Rieder said.

For fund investors, prevailing expectations now are that returns will mostly be a function of the interest earned, with little movement in prices. The Bloomberg Barclays U.S. Aggregate Bond index, the benchmark for most bond index funds, has a current yield of 2.5 percent. That suggests that you can probably expect to earn 1.25 percent or so in interest over the second half of the year.