Add month(s) to date, not to exceed the last day of the next month

I'm trying to add one or more months to a date field, but I'm running into an issue with the end of the month. If "today" is 01/31/2018, and I add one month, I would like the result to be 02/29/2018, but instead I get 03/03/2018.

Is there a way to calculate this, check to see if the date matches, and if it doesn't, set the date at the end of the previous month? In my example, 31!=3, so set the date at 02/29/2018 instead of 03/03/2018.

Here's the script that I'm using:

todayString = this.getField("today").valueAsString;

var months = Number(this.getField("months").valueAsString);

if (todayString=="" || months==0) event.value = "";

else {   

    var d = util.scand("dd.mm.yyyy", startDateString);

    d.setMonth(d.getMonth()+months);

    event.value = util.printd("dd.mm.yyyy", d);

}