What is an “extreme” limitation?
Social Security regulation 20 CFR 416.926a(e)(3) explains that a child has an “extreme” limitation in a domain when her impairment(s) interferes “very seriously” with her ability to independently initiate, sustain, or complete activities. A child’s day-to-day functioning may be very seriously limited when her impairment(s) limits only one activity or when the interactive and cumulative effects of her impairment(s) limit several activities. The regulations also explain that an “extreme” limitation also means:
- A limitation that is “more than marked”.
- The equivalent of functioning that would be expected on standardized testing with scores that are at least three standard deviations below the mean.
- A valid score that is three standard deviations or more below the mean on a comprehensive standardized test designed to measure ability or functioning in that domain, and her day-to-day functioning in domain-related activities is consistent with that score.
- For the domain of health and physical well-being, episodes of illness or exacerbations that result in significant, documented symptoms or signs substantially in excess of the requirements for showing a “marked” limitation.


