The effective federal funds rate (EFFR) is the volume-weighted median interest rate at which depository institutions lend reserve balances to other depository institutions overnight on an uncollateralized basis. It is calculated daily by the Federal Reserve Bank of New York. The series (FRED: DFF) begins in July 1954 and is one of the most closely watched indicators in financial markets because it directly reflects the Federal Reserve's monetary policy stance. The S&P 500 price overlay (left axis, log scale) shows how equities respond to rate changes over time. Gray bands mark NBER-designated U.S. recessions. Data sourced from FRED (Federal Reserve Bank of St. Louis).