[Solved]-How to set PointIntervals per month in HighChart-Highcharts

You can populate the xaxis value (by month) dynamically and push together with yxais data. The code would be like:

var s = {name: 'serial name', data: []}, 
    serialData = [], categories = [];
var flatData = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120], 
    startDate = Date.UTC(2000, 1, 1);
// Set the xaxis value as first day of month
for (var i = 0; i < flatData.length; i++) {
    var d = new Date();
    d.setTime(startDate);
    d.setMonth(d.getMonth() + i);
    categories.push(d.getTime());
}
for (var i = 0; i < flatData.length; i++) {
    s.data.push([categories[i], flatData[i]]);
}
serialData.push(s);

$('#canvas').highcharts({
    ......
    xAxis: { 
        type: 'datetime', 
    }
    serial: serialData
});

Then the xaxis labels would be 'by month'. Here is the example: JSFiddle.

The idea is imported from here: HighCharts Demo.

You can manually generate date tags and add them to the data list like this:

series: [{
        data: [["Jan 1, 2005", 0], ["Feb 1, 2005", 0], ..., ["Dec 1, 2005", 54.4]],
        pointInterval: 24 * 3600 * 1000 * 31,
        pointStart: Date.UTC(2005, 0, 01)         
    }]

This way, you can use the pointInterval as is (for approximate view on x-Axis), and use the tag on the chart dots (for the exact data).

If you zoom into the chart you will see slight overlap between the dots and the x-Axis ticks, but if you don't need perfect alignment this should do the trick.

To generate the date tags (e.g. "Jan 1, 2005") I would do something like this:

var data = [0, 0, 0, 0, 0, 0, 0, 148.5, 216.4, 194.1, 95.6, 54.4];
var date = new Date("January 1, 2005");
var monthNameList = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];

for (i = 0; x < data.length; i++)
{
   var stringDate = monthNameList[date.getMonth()] + " 1, " + date.getFullYear();
    resultList.push(stringDate);
    date.setMonth(date.getMonth() + 1);
}

Then add each item to the data.

Edited: I think the first answer above is a very neat way to generate date tags. (Check the JSFiddle)

The other answers to this are out of date.

Now all you need to do is add the pointIntervalUnit property. You can combine this with pointInterval to draw irregular intervals :

Highcharts.chart('container', {

...

plotOptions: {
    series: {
        pointStart: Date.UTC(2015, 0, 1),
        pointIntervalUnit: 'month'
    }
},
...

See: https://api.highcharts.com/highcharts/plotOptions.series.pointInterval

Also: https://jsfiddle.net/gh/get/library/pure/highcharts/highcharts/tree/master/samples/highcharts/plotoptions/series-pointintervalunit/