When should I worry about a speech delay? what are normal milestones for language and speech?

What the evidence says

There is a wide normal range, but general milestones look like this: cooing by 2 months, babbling by 6 months, first words around 12 months, understanding far more than they can say at 15-18 months, a 'language burst' starting around 18 months, and by 24 months most children use at least 50 words and start combining two words. By age 3, vocabulary grows to roughly 1,000 words and children use short sentences; by age 5, vocabulary reaches about 5,000 words with clear enough speech for strangers to understand almost all of it. Recognized red flags that warrant talking to your doctor include: no babbling by 9 months, no first words by 15 months, no consistent words by 18 months, no word combinations by 24 months, or speech that stalls or goes backward at any age.

Other flags are: you can't understand your child's speech at 24 months, strangers still can't understand them by 36 months, or your child doesn't seem interested in communicating at all. Also flag any drooling beyond what's expected, trouble sucking/chewing/swallowing, poor coordination of lips/tongue/jaw, or stuttering that causes real frustration or embarrassment. Because hearing loss is a common hidden cause of speech delay, any child with a suspected delay should have their hearing checked.

You do not need to wait for a doctor's referral in many places: in Ontario, for example, families can self-refer directly to the Preschool Speech and Language Program. Since language delay is common, affecting a meaningful share of toddlers, and can sometimes signal something else (like hearing loss, a broader developmental delay, or autism spectrum disorder), the practical advice everywhere is: if you're worried, get it checked rather than waiting to see if your child catches up.