Student or Learner
Do we need to add 'article a' to special events in calendar?
a happy new year
a merry christmas
Is it correct, article+adjective+day/month/year?
But why people say 'happy new year' without an 'A'? Is it acceptable?
If it's not an announcement/greeting, then you do need to say "I hope you have a happy New Year", "I want to wish you a happy Christmas".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.