How do I create a text field that auto-populates a date three years from the current date?

I am trying to create a PDF form that will auto-populate an expiry date three years in the future from the current date in a created text field.

Text field name: ExpDate

Text field format: mm/dd/yy

So far I have entered the following into Page Properties --> Actions --> Add an Action (Trigger = Page Open, Action = Run a JavaScript):

var ExpDate = new Date();

ExpDate.setYear(ExpDate.getYear()+3);

var f=this.getField("ExpDate");

f.value=util.printd("mm/dd/yy", ExpDate);

This will produce the correct expiry date on the day that I make the certificate (i.e. it will read 06/07/16 on June 7, 2016), but when I open it the next day it will still ready 06/07/16 instead of 06/08/16. I am sure it is something simple that I need to change. Any ideas?