The easiest way to do this is to change the height of the #container div to at least 500px. Highcharts will show the rest of the labels since there will be enough room.

You can make the font smaller, though in this case you will probably still need to increase the height to keep it readable. Here's how:

xAxis: {
    categories: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec','Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
    min: 6,
    labels: {
        style: {
            fontSize: '5px'

Here is a way to adjust the height of a graph based on the amount of data in the series. It might not be the best solution but it works. You'll have to adjust the values to your needs.

if (chart.series[0].data.length > 0) {
    var baseHeight = 150;
    var extraHeightPerThing = 25;

    chart.setSize(null, baseHeight + chart.series[0].data.length * extraHeightPerThing);

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