Increments for days/months on y-axis

Hello all,

This is gonna sound noobish, but I'd like some advise on how to set up days and months on the y-axis such that they are in increments. The obvious problem is that some months do not have exactly 30 days. So Excel, from what I've seen so far, will throw a random number of days. I just want it so that it shows 31 days for Jan, 28 days for Feb, 31 days for March, 30 for April etc. but show these as fixed, one month increments. Is it possible to have Excel show the months in increments?

Thank you in advance!