There is also a `-b` flag to get it back in to the shape you'd expect from cal. I find the week column easier to read in that form:

   w| Mo Tu We Th Fr Sa Su
  31|              1  2  3
  32|  4  5  6  7  8  9 10

[Said as someone who aliases cal to "ncal -wb" mostly just to get the correct first day of the week for their locale.]

¹ https://en.wikipedia.org/wiki/ISO_week_date