I’ve always heard that your IQ can vary slightly depending on how you feel that day, but I’m wondering how big that effect really is. Can being tired or stressed actually lower your score in a measurable way, or does it just make you feel less sharp? Has anyone seen research or personal experience showing how much performance can really swing from one day to another just based on fatigue or mindset?
Yes, fatigue and stress can definitely lower your score—typically around 5-10 points, but sometimes more if you’re really exhausted or anxious. Sleep deprivation hits especially hard on working memory and processing speed. Your “baseline” IQ is pretty stable though, which is why good testing conditions matter. If you’re having a rough day, it’ll show in your performance.
I’ve actually experienced this firsthand. I took an IQ test twice, once well-rested and once after several nights of poor sleep and work stress. What I noticed most was slower pattern recognition on matrix reasoning tasks, more careless errors from losing focus, and serious mental fatigue by the end sections. It’s hard to say how much was genuine cognitive impairment versus just lower motivation to push through difficult problems when tired. From what I’ve seen, swings of 5-10 points based on testing conditions seem pretty common, which matches my experience.