The European Central Bank’s benchmark interest rate, the rate it charges commercial banks to borrow cash, is already zero. There is still room for the bank to cut the so-called deposit rate, the rate commercial banks pay to deposit money at the central bank. The deposit rate is already minus 0.4 percent, in effect a penalty that prods banks to lend money rather than to hoard it at the central bank.

The negative rate also serves as a benchmark for the bond market, helping to drag down the interest that consumers ultimately pay on mortgages or car loans. The yield on 10-year German government bonds, considered the safest investment in Europe, has dipped below minus 0.4 percent. In effect, investors are willing to pay the German government to keep their money safe.

But analysts say that the deposit rate cannot go much lower without distorting money markets. And the central bank does not have that much room to buy more government and corporate bonds, another method of pushing down market interest rates. The European Central Bank already owns a huge chunk of the bond market as a result of its earlier stimulus programs.

By signaling action early, the central bank may be trying to get maximum impact from the tools it has left. Like firefighters running out of water, the bank’s policymakers are better off using what they have before the blaze gets even bigger.

Action now also effectively locks in policy well after Mr. Draghi’s term expires at the end of October. His successor, Christine Lagarde, the managing director of the International Monetary Fund, will not have much room to maneuver for her first year in office.

Ms. Lagarde, however, is seen as a supporter of Mr. Draghi’s approach to monetary policy. Financial markets will take comfort in knowing that the central bank will continue to do what it can to avoid recession even after Mr. Draghi leaves.

The European Central Bank’s Governing Council said Thursday that it had no objection to Ms. Lagarde’s appointment by European political leaders. Ms. Lagarde is “a person of recognized standing and professional experience in monetary or banking matters,” the council said in a statement.