What IQ is considered retarded
Executive summary
The clinical threshold historically tied to the derogatory word “retarded” has been an IQ roughly two standard deviations below the population mean—about an IQ of 70 (sometimes cited as 70–75)—but modern diagnosis of intellectual disability requires both low measured intellectual functioning and significant deficits in adaptive skills, and professional guidelines no longer rely on an IQ cutoff alone [1] [2] [3].
1. What the old shorthand meant and why the word is outdated
For decades the label commonly paraphrased by the question referred to the diagnostic category formerly called “mental retardation,” a term now retired because it is offensive and clinically imprecise; current manuals and advocacy groups use “intellectual disability” and emphasize functioning as well as test scores [1] [4].
2. The conventional IQ cutoff: around 70 (± measurement error)
Standardized IQ tests have a population mean of 100 and a standard deviation of 15; two standard deviations below the mean—about an IQ of 70—has been the conventional statistical threshold for identifying intellectual impairment, and some authorities note a practical band that can extend to 75 because of test error and confidence intervals [5] [1] [6].
3. How professional criteria have shifted: IQ is part of a bigger picture
Diagnostic frameworks such as DSM-5 and leading professional organizations stress that an IQ score alone is insufficient: clinicians must document limitations in adaptive behavior (daily living, communication, social skills) that began during the developmental period, which is why a fixed numeric label is no longer the sole arbiter of diagnosis [3] [1] [7].
4. Severity ranges historically tied to IQ scores
When IQ ranges were used to grade severity, common groupings placed mild intellectual disability roughly between IQ 50–70, moderate 35–50, severe 20–35, and profound below about 20–25, with most people with intellectual disability falling into the mild category (about 85%); these ranges appear in clinical literature and reference manuals but are now used as descriptive guides rather than strict diagnostic cutoffs [5] [8] [9].
5. Why simple cutoffs can mislead in real cases
IQ tests vary in which abilities they sample, subtest scores can diverge, and real-world adaptive skills may not track perfectly with a single full-scale score; clinicians therefore consider confidence intervals (often ±5 points), alternative composites (e.g., General Abilities Index), cultural and language factors, and co-occurring conditions when interpreting scores [10] [6] [3].
6. Practical takeaway for interpretation and language
In plain terms, an IQ around 70 (sometimes cited up to 75) signals a level of cognitive performance that—if accompanied by deficits in adaptive functioning beginning in childhood—meets long-standing clinical definitions of intellectual disability, but careful assessment and respectful language matter: the field no longer uses the slur reflected in the question and emphasizes supports tailored to strengths and needs [2] [3] [1].
7. Competing emphases and hidden agendas in reporting
Popular shorthand (and older educational or legal thresholds) can oversimplify and stigmatize; advocacy groups and clinicians push for function-focused diagnoses to reduce harm and ensure services, while some systems and benefits programs still rely on numeric cutoffs for eligibility, creating tension between clinical nuance and administrative convenience [3] [6] [11].
8. Limits of the available reporting
The provided sources document consensus ranges, historical cutoffs, and the contemporary pivot away from IQ-alone diagnosis, but they do not settle every borderline case nor provide jurisdictional rules that determine benefits or legal status in every country—those specifics require local policy references not included here [5] [6].