— Age & cognition

IQ at age 40 — what's typical?

IQ scores at age 40 are age-normed — meaning your raw test performance is compared against other 40-year-olds (or the closest reference cohort), then converted to a scaled score with population mean 100 and SD 15. The "average IQ at age 40" is therefore always 100 by construction.

Modest decline in fluid intelligence (~0.5 SD below 25-year-old peak). Crystallised intelligence still climbing. Wisdom and judgement compensate substantially in real-world performance.

How IQ measurement works across ages

Modern IQ tests use age-normed scoring. A 10-year-old answering correctly on items that 12-year-olds typically get right scores higher than 100 (above their age-mates). A 30-year-old answering those same items correctly scores exactly 100 (typical for their age group). The score is always a comparison to peers, not an absolute capability.

Cognitive trajectories across the lifespan

• Fluid intelligence — peaks in early 20s, gradually declines 0.5-1 IQ point per decade after
• Crystallised intelligence — rises until 60s or 70s, then slow decline
• Processing speed — peaks early 20s, steepest age-related decline of any cognitive index
• Working memory — gradual decline from mid-30s onward
• Vocabulary, judgement, applied wisdom — typically rise through mid-life

How 40 compares to other ages

• IQ at age 12 — Early adolescence
• IQ at age 15 — Mid adolescence
• IQ at age 18 — Late adolescence / early adult
• IQ at age 21 — Young adult
• IQ at age 25 — Young adult