Returns true if a date variable is after another date. That second date can be the name of another variable or a literal date string.
start_date: January 17 2015
end_date: December 1 2015
{{ if end_date | is_after:start_date }}
{{ if start_date | is_after:2014 }}
{{ if start_date | is_after:end_date }}
true
true
false