The person you’re talking with is older than you
You aren’t really close with that person
You are unsure which form to use
You can also use the honorific version and say “saengshin chukha-deuryeoyo“ (in Hangul: 생신 축하드려요) if the person you’re saying it to is considered “higher status” (a rather complex concept) and in real life, you would for example say this to:
An older relative
Your teacher
For friends and close ones, however, you will want to use the phrase: