A parent almost always understands their own child. So the useful question is not “do I understand them”, but how much is understood by someone hearing them for the first time.
The rule of quarters
The most frequently cited guide comes from Coplan and Gleason (1988): at 1 year an unfamiliar listener understands about 25% of what is said, at 2 years about 50%, at 3 years about 75%, and at 4 years almost all of it.
What newer measurements show
Hustad and colleagues (2021) did not rely on parents’ estimates. They measured how much unfamiliar listeners actually understood from recorded speech of typically developing children. For an average child, sentence intelligibility reaches 50% at about 2 years 10 months, 75% at about 3 years 10 months, and 90% at about 5 years 2 months.
The difference between the two sources matters: a four-year-old may still get individual sounds wrong, but the message should be clear. Perfect articulation and intelligibility are not the same thing.
When it is worth checking
- At 3 years an unfamiliar person understands less than half of what is said.
- The child often has to repeat themselves, or gets upset when not understood.
- They start to go quiet or avoid speaking in new situations.
Sources
- Coplan, J. & Gleason, J. (1988). Unclear speech: recognition and significance of unintelligible speech in preschool children. Pediatrics.
- Hustad, K. et al. (2021). Speech development between 30 and 119 months in typical children. Journal of Speech, Language, and Hearing Research.
- American Speech-Language-Hearing Association (ASHA) — asha.org
This article is an informational summary of published research and does not replace an individual assessment.