Six systems, side by side
Each bar is one system's bands from IQ 40 to 170. The line is your score; the highlighted band is what it was called. Hover a band for its range.
The 2008 adult scale kept 10-point bands centred on 100 and still used 'Borderline' for 70–79 and 'Very superior' for 130+.
The manual stresses that labels describe the score, not the person, and should be read with the confidence interval.
Checked Oct 2026: Wechsler-Bellevue bands and shares (128+ = 2.2%, 120–127 = 6.7%, 111–119 = 16.1%) as quoted from Wechsler's Measurement of Adult Intelligence; WAIS-IV and SB5 tables (SB5 "very gifted" corrected to 140+); Terman's top bands (140+, 120–140) match standard reproductions. DSM-IV ranges are approximate and overlap by design.
Ratio IQ broke for adults; the deviation IQ fixed it
Terman's IQ divided mental age by real age. That works while children's performance grows every year, but adult test performance levels off in the late teens. Divide a flat mental age by a rising real age and every adult appears to decline. Terman's workaround capped the real-age divisor at 16.
Wechsler dropped the ratio altogether. A deviation IQ ranks you against people your own age, so a 40-year-old and a 9-year-old with IQ 115 are both one SD above their peers. Every modern band is set on that footing.
How likely is IQ 128 to belong in each WAIS-IV band?
Every score carries measurement error. A full-scale Wechsler IQ has a standard error of roughly 2–3 points; short screeners and online tests run nearer 5 or more. Near a band edge, the honest label is "probably X, possibly Y". Reports therefore give a confidence interval, and good ones name both bands when the interval crosses a line.
Clinical terms that became insults, and what replaced them
Listed for history only. Current systems (DSM-5, ICD-11) define intellectual disability by both measured ability and adaptive functioning, and grade severity mainly on adaptive functioning.
"Gifted" has no single line
School programmes pick cut-offs from about 120 to 130, often as a percentile, and many add achievement or teacher ratings. Beyond 130, Miraca Gross's levels (moderately, highly, exceptionally, profoundly gifted) are widely quoted, even though tests rarely measure reliably that far out.
Three decisions that need more than a score
A score of 68 alone is not a diagnosis; a score of 72 does not rule one out.
Cut-offs vary by district and country; the band label is rarely the gate.
Older 'IQ–achievement discrepancy' rules have largely given way to response-to-intervention approaches.
- Terman, L. M. (1916). The Measurement of Intelligence. Houghton Mifflin.
- Wechsler, D. (1939). The Measurement of Adult Intelligence. Williams & Wilkins.
- Roid, G. H. (2003). Stanford-Binet Intelligence Scales, Fifth Edition: Technical Manual. Riverside.
- Wechsler, D. (2008, 2014). WAIS-IV and WISC-V Technical and Interpretive Manuals. Pearson.
- American Psychiatric Association (1994; 2013). DSM-IV and DSM-5.
- Gross, M. U. M. (2004). Exceptionally Gifted Children (2nd ed.). RoutledgeFalmer.
- Rosa's Law, Pub. L. 111-256 (2010).
- World Health Organization (2019/2022). ICD-11: Disorders of intellectual development (6A00).
- Schalock, R. L., Luckasson, R., & Tassé, M. J. (2021). Intellectual Disability: Definition, Diagnosis, Classification, and Systems of Supports (12th ed.). AAIDD.