Only two birthday celebrations are referred to in the Bible. Interestingly, each one is associated with a tragic event (see Genesis 40:20-22; Mark 6:21-27). Equally interesting is the fact that there are no examples in the Bible of any man or woman of God having participated in a celebration of his or her own birthday. Not once do we find that Jesus marked the anniversary of His birth in any fashion.
The Bible reveals that celebrating our physical birth is not an issue of primary importance to God. He is far more concerned with the development of spiritual character within us and our being born into His Kingdom (Ecclesiastes 7:1; Revelation 21:7; Romans 2:7; John 12:24-25). It is evident that God does not want His people to mimic the world in a self-serving and greedy approach. This certainly includes what one thinks about and how one treats the anniversary of one's birth.
It is good to consider, however, that there is a vast difference between a simple acknowledgment that someone is a year older and observing the fact with a celebration. The date of one's birth is not pagan. The fact that someone is a year older is not pagan. The giving of gifts is not of pagan origin. Certainly, there are a number of milestones in life which are significant. A person's reaching teenage or becoming old enough to drive or becoming of age or becoming seventy or eighty are all events which are perfectly proper for family members and friends to acknowledge. Simple recognition of an achievement is not wrong.
On the other hand, a birthday celebration with its usual trappings, inviting guests, giving elaborate gifts, baking and decorating a cake, lighting candles, and so forth, is an entirely different matter. This kind of festivity tends to accentuate flattery and vanity—the I-me-my attitude—and the get rather than the give way of life. Vanity and glorifying the self, of course, are condemned in God's Word (see Galatians 5:26; II Peter 2:18; Colossians 2:18; I Corinthians 5:6; and Psalm 24:3-4).