The date fields use a string format like this: 2016-04-18
You can strip off the year using the substring function. Try substring(field,5,5). Then you can compare that to 02-16 and/or 03-15.
To do a numeric comparison, you can remove the hyphen (-) character using the translate(field,"-", "") command and number function. You'll need another field in your form to take the result.
We can help with this and it won't take much support time.
Good luck!