[Solved]-adding labels exactly above x-axis categories in highcharts-Highcharts

You can render the text once, then look at the bounding box of the Element to determine the width of the text, and then use this information to create a correctly positioned text by rendering it again.

For example:

var element = r.text('19% yoy increase ', 0 , 0)
.css({
    fontSize: '11px'
}).add();

var width = element.getBBox().width;
element.destroy();

r.text('19% yoy increase ', data[0].plotX + chart.plotLeft - (width/2) , startY)
.css({
    color: '#4572A7',
    fontSize: '11px'           
}).add();

See this JSFiddle for a demonstration.