Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link
Levels of Intellectual Disability

Levels of Intellectual Disability


IQ Range

Ability at Preschool Age (Birth to 6 Years)

Adaptive Skills at School Age (6 to 20 Years)

Support Required at Adult Age (21 Years and Older)


IQ 52–69

Often presents as speech–language delay

Often not diagnosed until later age

Can develop social and communication skills

Some difficulty learning reading, writing, and math, but can learn up to about the 6th-grade level by late adolescence

Challenges making plans and managing money

Socially immature but can be expected to learn appropriate social skills

Some limitation of judgment and understanding of risk—more easily manipulated by others

Needs guidance and assistance in complex tasks (such as health care and legal decisions) and during times of unusual social or economic stress

Can usually achieve enough social and vocational skills for self-support


IQ 36–51

Poor social awareness

Can profit from training in self-help

Can talk or learn to communicate

With support, can progress to elementary school level in schoolwork

May learn to travel alone in familiar places

Social judgment and understanding limited but can learn some social and occupational skills

May have successful friendships and romantic relationships

Cares for simple personal and household needs after extended guidance

Needs supervision and guidance managing money, scheduling, and all but simplest daily tasks

May achieve self-support by doing unskilled or semiskilled work in a supportive environment


IQ 20–35

Able to learn some self-help skills

Has limited speech skills

Can say a few words

Can talk or learn to communicate about simple, everyday events and learn simple health habits

Little understanding of written language, numbers, time, or money

Benefits from habit training

Usually successful relationships with family members and familiar others

Sometimes maladaptive behavior (including self-injury)

Can develop some useful self-protection skills in controlled environments

Requires support for all daily tasks but may contribute partially to self-care under complete supervision


IQ 19 or below

May need nursing care due to limited self-care skills

Extreme cognitive limitation

Often sensory and/or physical impairments

Limited understanding of speech or gestures; communicates mainly nonverbally

Enjoys company of well-known family and caretakers, but sensory and physical impairments often limit social activities

Often needs nursing care

May have very limited participation in self-care