Grafna group by month

Hi All,

I am trying to use the group by time function for my influx data on Grafana graph chart, there is no group by month feature provided so i use group by(30d) to show my aggregate data every 30 days, but from the point on the graph chart, the last point is not today, any one knows how influxdb calculate the start date in the group by time function? also i try to use the offset like group by(30d,16d) but that means u need to change the offset valu e every day.

not sure influxdb supports it