Girls typically start puberty between ages 8 and 13, while boys start between ages 9 and 14. Within those ranges, there’s a lot of normal variation. Your child might be the first in their class to show changes or one of the last, and both scenarios are usually perfectly fine.
When Puberty Starts in Girls
The first visible sign of puberty in girls is breast budding, small firm lumps beneath one or both nipples. This most commonly appears between ages 8 and 13, with many girls noticing it around age 9 or 10. Pubic hair usually follows shortly after, though some girls develop hair first.
A girl’s first period arrives later in the process, typically about two to two and a half years after breast development begins. Current CDC data puts the median age of a first period at 11.9 years. About 10% of girls get their period by age 10, roughly half by age 12, and 90% by age 14. These numbers have shifted slightly earlier over recent decades: in 1995, the median age was 12.1, and only 7% of girls had their period by age 10 compared with 10% today.
Growth spurts in girls tend to happen early in puberty, often peaking before the first period. Most girls reach their adult height within one to two years after menstruation starts.
When Puberty Starts in Boys
The first sign of puberty in boys is growth of the testicles, which typically begins between ages 9 and 14. It’s a subtle change that often goes unnoticed. Pubic hair, body odor, and a deepening voice follow over the next year or two.
Boys hit their growth spurt later in puberty than girls do, which is why many boys in middle school are temporarily shorter than their female classmates. Peak height gain for boys usually happens around ages 13 to 15, and most continue growing into their late teens.
Facial hair, a more adult body shape, and the completion of voice changes tend to come toward the end of the process. From first signs to full physical maturity, puberty in boys can take anywhere from two to five years.
What Triggers Puberty
Puberty starts in the brain, not in the reproductive organs. A region deep in the brain begins releasing a signaling hormone in rhythmic pulses. Those pulses tell the pituitary gland (a pea-sized structure at the base of the brain) to release two other hormones into the bloodstream. In girls, these hormones signal the ovaries to produce estrogen. In boys, they signal the testes to produce testosterone. All the physical changes of puberty, from growth spurts to body hair, are downstream effects of this hormonal chain reaction.
What makes the brain flip this switch at a particular age isn’t fully understood, but genetics plays the biggest role. If a parent started puberty early or late, their child is more likely to follow a similar timeline.
How Body Weight Affects Timing
After genetics, body weight is one of the strongest influences on when puberty begins. A large Kaiser Permanente study found that children who develop obesity at a young age are more likely to start puberty earlier than children at a healthy weight.
The effect is especially pronounced in girls. Girls with severe obesity at ages 5 to 6 had a 63% greater risk of earlier breast development and were 2.6 times more likely to get their period before age 12 compared with girls at a healthy weight. Among girls with severe obesity, Black girls showed signs of pubic hair about 12 months earlier, Asian and Pacific Islander girls about 11 months earlier, and white girls about 8 months earlier than their healthy-weight peers.
Boys show a similar pattern, though the shift is smaller. Boys with severe obesity had a 23% higher risk of earlier testicular development and a 44% higher risk of earlier pubic hair growth. White boys with severe obesity showed pubic hair about 7 months earlier than healthy-weight boys, and Black boys with obesity about 6 months earlier.
The connection likely involves fat tissue’s role in hormone production. Fat cells produce a small amount of estrogen and release signaling molecules that can influence the brain’s puberty trigger. This is also why very low body weight or intense caloric restriction can delay puberty.
Early Puberty: When to Pay Attention
Puberty is considered early (called precocious puberty) when signs appear before age 8 in girls or before age 9 in boys. This isn’t just about being on the younger end of normal. Precocious puberty can affect a child’s final adult height because the growth plates in bones close earlier when sex hormones rise too soon. It can also create emotional and social challenges when a child’s body is developing years ahead of their peers.
In most cases, especially in girls, early puberty has no identifiable medical cause. It’s simply the brain activating the process sooner than average. Less commonly, it can be linked to a structural issue in the brain or a problem with the adrenal glands or ovaries. A pediatrician can determine whether evaluation is needed based on the child’s age, how quickly changes are progressing, and whether growth patterns look unusual.
Late Puberty: When to Pay Attention
Puberty is considered delayed when girls show no breast development by age 13 or boys have no testicular growth by age 14. For girls specifically, not having a first period by age 15 also warrants evaluation, even if other signs of puberty are present.
The most common cause of delayed puberty is constitutional delay, meaning the child is a “late bloomer” who will go through puberty normally, just on a later schedule. This tends to run in families. Less often, delayed puberty signals an underlying condition such as a thyroid issue, a nutritional deficiency, or a problem with hormone production.
Late puberty is more common in boys than girls, and it’s more likely in children who are very thin or who train intensively in sports. Most kids with delayed puberty catch up fully and reach normal adult development, though the timeline can feel stressful in the moment.
The Wide Range of Normal
One of the most important things to understand is that a five-year spread in starting age is completely typical. A girl who begins developing at 8 and a girl who begins at 12 are both within the normal range. The same is true for a boy at 9 versus a boy at 14. Puberty also doesn’t progress at the same speed for everyone. Some kids move through all the stages in two years, while others take four or five.
The order of changes matters more than the exact age. In girls, breast development before pubic hair before the growth spurt before the first period is the classic sequence. In boys, testicular growth before pubic hair before the growth spurt before facial hair is typical. When changes happen out of the expected order, or when puberty seems to stall partway through, that’s a more meaningful signal than simply starting on the early or late side of average.