14/05/2026
This page, written by renowned speech-language pathologist Caroline Bowen, covers speech intelligibility milestones in children, essentially, how clearly kids should be speaking at various ages.
Here's a breakdown:
What is intelligibility?
Intelligibility refers to speech clarity, the proportion of a speaker's output that a listener can readily understand. In typical development, this increases as children learn to talk.
Early milestones (Lynch et al., 1980):
By 18 months, a child's speech is normally 25% intelligible; by 24 months, 50–75%; and by 36 months, 75–100%.
More recent research (Hustad et al., 2021):
For average children (50th percentile), single-word intelligibility is expected to reach 50% by 31 months, 75% by 49 months, and 90% by 83 months. Multi-word intelligibility develops slightly faster, reaching 90% by about 62 months. The researchers also found considerable variability among typical children, with intelligibility growth continuing through age 9 for some, and that children should be at least 50% intelligible by 48 months.
Intelligibility to strangers (Coplan & Gleason formula):
A simple guide: divide the child's age in years by 4, then multiply by 100 to get the expected percentage understood by strangers, so a 2-year-old should be about 50% intelligible to strangers, and a 4-year-old should be fully intelligible.
When to seek intervention:
Children over age 4 with intelligibility below 66% should be considered candidates for intervention, meaning unfamiliar listeners should be able to understand at least two-thirds of what a 4-year-old says.
Clinical rating scale:
A simple 5-point scale is used clinically, ranging from "completely intelligible" (1) to "completely unintelligible" (5), which is useful for tracking a child's progress over time.
Dr Bowen's page is a practical reference for parents and clinicians to gauge whether a child's speech clarity is on track for their age.
https://www.speech-language-therapy.com/index.php?option=com_content&view=article&id=29%3Atable1&catid=11%3Aadmin&Itemid=101&