When does the fontanelle close?

The anterior fontanelle—commonly known as the “sky gate” or “crown fontanelle”—is located at the center of an infant’s scalp. When gently palpated, you will feel a soft, slightly depressed area on the top of the baby’s head; this is the anterior fontanelle. In contrast, the posterior fontanelle, situated at the back of the head (near the occiput), is nearly closed at birth, whereas the anterior fontanelle closes much later. So, what is the earliest age at which the anterior fontanelle may close?

When Does the Fontanelle Close?

Fontanelles refer to the gaps between incompletely ossified cranial bones in infants and young children. There are two main fontanelles—the anterior and posterior—and the timing of closure depends on each.

1. Anterior fontanelle: Located at the top of the skull, it is a diamond-shaped gap formed by the sutures between the two frontal bones and the two parietal bones. At birth, its diagonal measurement typically ranges from 1.5 to 2.5 cm. As the infant’s head grows and head circumference increases during early development, the anterior fontanelle may initially enlarge slightly. After approximately six months, progressive ossification of the cranial bones causes it to gradually shrink, and it usually closes between 12 and 18 months of age.

2. Posterior fontanelle: Situated near the occiput, it is a triangular gap formed by the sutures between the two parietal bones and the occipital bone. Normally, it is either very small or already closed at birth—often barely large enough to accommodate the tip of one finger—and typically closes no later than 6–8 weeks after birth.

Fontanelle closure is influenced by both cranial bone ossification and brain development, making it an important clinical indicator of an infant’s overall growth and health. Observing changes in the fontanelle can facilitate early detection, diagnosis, and treatment of various medical conditions. Therefore, parents should closely monitor their baby’s fontanelle development.

In fact, premature fontanelle closure in most infants is not due to pathological causes but rather results from excessive calcium supplementation administered by caregivers. Hence, mothers should ensure appropriate, medically guided calcium supplementation for their infants—not indiscriminate or prolonged supplementation—and schedule regular follow-up assessments after initiating supplementation.

We hope the above information is helpful. Wishing you a happy and healthy life!