mapping & loops - counting up or counting down
You can accomplish your task using only core Javascript, with no reference to JQuery code, in about that many lines. JQuery is overkill for this task. 

I applied the following changes to make your code more readable:


Reduced knowledge required to understand it (removed JQuery).
Reduced the complex portions (see iCurrentOvertime).
Added Hungarian notation; i.e. prepending integers with "i", arrays with "a", etc.
Encased added values together within parentheses (e.g. iCurrentHours+iTotalHours becomes (iCurrentHours+iTotalHours)).


The new code is below:

function calculateOvertime(days) {
  var aHours = [];
  var iTotalHours = 0;
  for(var i=0;i&lt;days.length;i++){
    var iCurrentHours = days[i];
    var iNewHours = (iCurrentHours+iTotalHours);
    var iCurrentOvertime = Math.max(0,(iNewHours - Math.max(iTotalHours,40)));
    iTotalHours = iNewHours;
    aHours.push({
      reg: (iCurrentHours - iCurrentOvertime),
      ot: iCurrentOvertime
    });
  }
  return aHours;
}
calculateOvertime([16,16,16,16]);