noun
birthday
A1
'Geburtstag' means 'birthday'. It's a masculine noun (der) with plural 'Geburtstage' and genitive singular 'des Geburtstags'. Common phrase: 'am Geburtstag' (on one's birthday). Often used with feiern: 'einen Geburtstag feiern'. Regular declension; no irregular plural. Used to mark the annual anniversary of birth and celebrations.
Examples
Ich habe Geburtstag.
It's my birthday.
Mein Geburtstag ist im Juli.
My birthday is in July.
Die Kollegen organisierten eine Überraschung, weil ihr Geburtstag in einer Woche war.
The colleagues organized a surprise because her birthday was in a week.
Details
Mnemonics
Picture a birthday cake with candles — 'Geburtstag' is the day of birth celebration
Der Geburtstag — many -tag (day) nouns are masculine (der Montag, der Tag)