Speech other people can understand
Strangers can understand about half of what most children say by around 3 years, and most of what they say by around 4. Children vary a lot: some get there a year or more later.
How sure are we?
Fairly sure. Two large studies, but they measured this in very different ways and found quite different ages. How we know this
What it’s a sign of
Your child's speech is becoming clear enough for people who don't know them to follow.
When parents are asked, they report strangers understanding most of their child's speech much earlier: in a study in four countries, half of parents said so by about 2½ years. When researchers ask adults who don't know the child to write down exactly what they say, the ages come about a year later. Everyday conversation, where listeners can guess from what's going on, is easier to follow than these tests. The CDC lists talking well enough for others to understand most of the time at 3 years.
The study that measured this directly tested children from 2½ years, so we don't know how clear the youngest talkers are, and it was done in one country.
A main source for the ages
Speech Development Between 30 and 119 Months in Typical Children I: Intelligibility Growth Curves for Single-Word and Multiword Productions
Katherine C. Hustad, Tristan Mahr, Phoebe Natzke, Paul J. Rathouz · 2021 · Journal of Speech, Language, and Hearing Research
- Children
- 538 children
- Where
- The United States (run at the University of Wisconsin–Madison)
- Ages
- 2½ to almost 10 years
- How
- Children said words and sentences, and adults who didn't know them wrote down what they heard
- What it found
- For a typical child, strangers understood half of the words in their sentences by about 34 months and three-quarters by about 46 months. Nearly all children (all but the slowest 5 in 100) reached these levels about a year later.
- Limits
- Children were tested repeating set words and sentences, which can be harder to understand than everyday talk. It was done in one country.
A main source for the ages
Similarities and differences in child development from birth to age 3 years by sex and across four countries: a cross-sectional, observational study
Ilgi Ozturk Ertem, Vibha Krishnamurthy, Mphelekedzeni C. Mulaudzi, Yanina Sguassero, Hakan Balta, Ozlem Gulumser · 2018 · Lancet Global Health
- Children
- About 4,900 healthy children
- Where
- Argentina, India, South Africa and Turkey
- Ages
- Birth to 3½ years
- How
- Trained staff asked parents open questions about what their child could do, at health clinics
- What it found
- Found the age by which half of children reached more than 100 milestones. Most came at similar ages in all four countries, and for boys and girls. For example, half of children waved bye-bye by about 11 months and said a first word by about 9 months.
- Limits
- Only four countries and no rural areas, children from city clinics, and only healthy children (about half of those who came were left out for health reasons). It gives the age for half of children, not the full spread.
A main source for the ages
Evidence-Informed Milestones for Developmental Surveillance Tools
Jennifer M. Zubler, Lisa D. Wiggins, Michelle M. Macias, Toni M. Whitaker, Judith S. Shaw, Jane K. Squires, Julie A. Pajek, Rebecca B. Wolf, Karnesha S. Slaughter, Amber S. Broughton, Krysta L. Gerndt, Bethany J. Mlodoch, Paul H. Lipkin · 2022 · Pediatrics
- Children
- A review of 34 studies and common checklists, not one group of children
- Where
- Studies from many countries (14 of the 24 with age data were from countries where English isn't the main language)
- Ages
- 2 months to 5 years
- How
- Experts reviewed studies and checklists, then placed each milestone at the check-up age by which about 3 in 4 children do it
- What it found
- Places calling a parent "mama" or "dada" at 12 months, and saying 1 or 2 other words at 15 months. These are ages by which about 3 in 4 children have started, rounded up to a check-up age.
- Limits
- Experts' judgement set the ages, and some milestones rest on opinion rather than measured ages. The lists haven't been tested to see whether they help.
If you’re worried about your child, talk to your child and family health nurse or GP.
Last checked 2 November 2026