After seeing cash rates rise throughout 2017 and 2018 — the first signs of life since the financial crisis for savers seeking safe and liquid income — rates slumped in 2019 in sync with the Fed’s rate cuts. For example, in December 2018, the online Ally bank offered a certificate of deposit that guaranteed a 3.1 annual yield for five years, which was well above the rate of inflation. A five-year Ally C.D. bought in December paid a 2.15 percent yield.

Mr. Tumin says high-yield savings accounts from online banks and credit unions offer the “most bang for the buck” for savers today. While brick and mortar banks and credit union savings accounts pay less than 0.2 percent on average, there are plenty of online savings accounts with yields ranging from 1.7 percent to above 2 percent.

Despite that risk-free opportunity to bolster cash performance, Christopher Cordaro, chief investment officer of RegentAtlantic financial advisers, says he sees plenty of new clients who are “earning next to nothing at their brick and mortar.”

He says he has taken on clients who had more than $1 million in an old-school bank account with virtually no yield. That inertia works out to a self-imposed penalty of $17,000 to $20,000, which is about what $1 million can earn if it is moved to a high-yield savings account.

Mr. Cordaro also says savers are probably leaving cash on the table in their brokerage accounts. “Brokerage firms have gone to charging zero commission on trades, but they can afford to do that by basically paying nothing on your sweep account,” said Mr. Cordaro, referring to the cash account where proceeds from trades are parked.

According to Crane Money Fund Intelligence, the average brokerage sweep account had a yield of 0.13 percent in December. Money-market mutual funds offered by those same brokerage firms — but not the default option — paid more than 1 percent.

For example, making a low-yielding bank account the default option for cash accounts has become a major revenue generator for Schwab. A $100,000 balance in a Schwab sweep account had a 0.06 percent yield in December. Alert investors who move their cash into a Schwab money-market account could earn more than 1.5 percent in December.