Subject + 的 + 生日
The noun 生日 (shēngrì) means "birthday" and refers to the anniversary of the day someone was born. It is used in both casual and formal contexts, often with 的 to indicate whose birthday it is.
今天是妈妈的生日,我们一起吃蛋糕吧。
Jīntiān shì māma de shēngrì, wǒmen yīqǐ chī dàngāo ba.
Today is Mom's birthday; let's eat cake together.
你的生日是几月几号?
Nǐ de shēngrì shì jǐ yuè jǐ hào?
What month and day is your birthday?
朋友们给我办了一个惊喜生日派对。
Péngyǒumen gěi wǒ bàn le yī ge jīngxǐ shēngrì pàiduì.
My friends threw me a surprise birthday party.