<a href="http://www.google.com/calendar/event?
action=TEMPLATE
&text=[event-title]
&dates=[start-custom format='Ymd\\THi00\\Z']/[end-custom format='Ymd\\THi00\\Z']
&details=[description]
&location=[location]
&trp=false
&sprop=
&sprop=name:"
target="_blank" rel="nofollow">Add to my calendar</a>