I have three selection drop downs in a form comprising of day, month, year. Pretty standard. Ive omitted all the individual select options for the purposes of this question.

<label for="start_date">Start Date<font class="required">*</font>:</label>
<select name="place_booking[day_val]">
<select name="place_booking[month_val]">
<select name="place_booking[year_val]">

Underneath this i have a selection for the number of days the client wishes to stay at the letting.

<label for="number_of_days">Number of Days<font class="required">*</font>:</label>
<select name="place_booking[number_of_days]">

Underneath there is a space to display the departure date based on there two selections above.

<label for="departure_date">Departure Date<font class="required">*</font>:</label>

? - this bit i would like to display the calculated date after the above is selected

Any help would be grealty appreciated.