[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.