To,

Name [name of the recipient]

Apartment name [name of the residential building or apartment along with the apartment number]

Street address [street name along with street number]

City [name of the city]

Subject [mention the subject which is usually to give birthday wishes]

Date [date on which the letter is being written]

Dear [name of the recipient. If the recipient is related you can mention the relation and if it is a formal birthday letter you have to give the appropriate salutation]

1^st paragraph: [in the first paragraph mention that you want to wish the person a very happy birthday and give him greetings]

2^nd paragraph: [in the second paragraph mention that what do you want the person to achieve on his birthday or you can advise him how to celebrate his birthday]

3^rd paragraph: [in the third paragraph give him blessings and best wishes]

Regards,

Name [name of the sender]

Address [address of the sender]