The Federal Reserve's policy rate. Almost every other consumer rate moves with it, some instantly and some with a lag.
The federal funds rate has barely moved over the past month, holding near 3.63%.
That is 0.70 percentage points below where it stood a year ago.
Today's reading sits at the bottom of its 12-month range of 3.63% to 4.33%.
At 3.63%, every quarter-point move by the Federal Reserve changes the interest on a $30,000 variable balance by about $75 a year.
Source: Federal Reserve Economic Data, series FEDFUNDS. National average, not a personalised quote.