The Rebbe's guidance on birthdays — a personal Rosh Hashanah — and how to mark them:
A personal Rosh Hashanah. A birthday is a personal Rosh Hashanah, a time for good resolutions and spiritual growth (IK 2066, 5822, 6268). It is a time of added spiritual strength and blessing — one's mazal is strong (IK 5089, 3714) — and a time to reconnect with the Tree of Life (IK 2741). Increasing in Torah and mitzvos on one's birthday brings blessing, spiritual and material (IK 8918, 9054, 10103).
The customs. On one's birthday: receive an aliyah to the Torah (on the Shabbos before, if the day itself has no reading), give tzedakah before prayer, say Tehillim — including one's own chapter — learn extra Chassidus and share it at a gathering or farbrengen, and take on a new good practice (IK 1548, 2097, 2146, 4082, 2761, 9777). Spend time reflecting, and strengthen one's Torah study and choice of good friends (IK 2993, 2226). Avoid wasting time (IK 7211). A birthday is a good time to begin wearing Rabbeinu Tam tefillin, when appropriate (IK 2279, 650, 2210).
Children's birthdays. Children too should mark their birthdays by growing in Torah, respect for parents and teachers, and good conduct (IK 9261, 10051, 8906). A boy approaching bar mitzvah should mark his birthday with tzedakah and extra learning (IK 6673). The upsherin is held on or near the third birthday (IK 3384, 8532; see Parenting – Naming a baby and the upsherin).
Milestone birthdays. Milestone birthdays — twenty, twenty-two, sixty, seventy — are times for special reflection and new growth (IK 650, 763, 8197, 9871); advancing age brings new opportunities (IK 1174).
See also: Prayer – Saying Tehillim; Parenting – Naming a baby and the upsherin; Emotional well-being – Growing older and retirement.