Plotting With Custom X Axis Labels in R -- Part 5 in a Series Unfortunately, while R understands our X axis data as dates, it doesn't choose optimal labels for our purposes. Instead, let's try labeling the first day of the month in each business quarter. To do this, we use the format function on dates to pick out the first (day 01) of every month, and select months 1,4,9, and 12 for the business quarters.