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Free tool · for SLP students and clinicians

MLU calculator

Paste a language sample with one utterance per line. The calculator applies Brown's counting rules, shows the morpheme count for each utterance so you can check it, and compares the MLU with Brown's stages and the Miller and Chapman (1981) age predictions.

This tool is general information for families and students. It is not a screening or diagnostic tool, does not give individual advice, and is not a substitute for an assessment by a registered speech-language pathologist. Automatic morpheme counting approximates Brown's rules and should be verified for clinical use. If you are worried about your child's communication, Ontario families can self-refer to their local Preschool Speech and Language Program at no cost.

Sources: Brown, R. (1973). A First Language: The Early Stages. Harvard University Press.; Miller & Chapman (1981), The relation between age and mean length of utterance in morphemes, JSHR

Frequently asked questions

How many utterances do I need?
Brown recommended 100 consecutive intelligible utterances. Fifty is common in clinical practice and gives a reasonable estimate. Fewer than 25 is unreliable.
Which rules does the calculator follow?
Brown's (1973) rules: inflections -s, -ed, -ing and possessive 's count as separate morphemes; contractions such as it's and don't count as two; compounds, proper names, ritualized reduplications (night-night) and irregular past tense (went) count as one; fillers (um, uh) are not counted; a stutter or false start counts the word once. Automatic counting can miss edge cases, so check unusual words by hand.
What do Brown's stages mean?
Brown divided early grammar into five stages by MLU: Stage I (1.0 to 2.0), II (2.0 to 2.5), III (2.5 to 3.0), IV (3.0 to 3.75) and V (3.75 to 4.5), with approximate ages from 12 to 46 months. They describe the typical order in which grammatical forms appear.
Is MLU reliable for every child?
MLU is most useful between roughly 18 months and 5 years. It levels off around 4 to 5 and is affected by dialect, bilingualism, sampling context and how utterances are segmented. Treat it as one measure among several.

Go further

MLU and Brown's stages (full guide) PCC calculator SLP glossary

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