Why Is Average IQ 100? How the Scale Was Built
Why is average IQ 100? Because test makers set it there on purpose. An IQ test compares your answers with a large sample of people your age, and the scoring is built so the middle of that sample always comes out as 100, with 15 points marking each standard step away from it.
It's a bit like setting the zero on a thermometer: the number is a reference point, not a measurement of how smart "normal" is. If you'd like to see where your own reasoning sits compared with that middle, and which skills to work on, IQ Tester shows you in about two minutes: Find my weak spots.
Short answer: it is set to 100 on purpose
Nobody discovered that people "have 100 IQ" the way you'd discover the boiling point of water. The number 100 was picked as a convenient middle, and every well-made test is scaled so its average lands there.
That's why:
- Is average IQ always 100? On a properly normed test, for the group it was normed on, yes.
- What is a normal average IQ? 100, with most people between 85 and 115.
- What's the average IQ of a normal person? By definition, 100 for their age group.
Where did 100 come from?
In the early 1900s, tests used a "ratio IQ": your mental age divided by your real age, times 100. A child performing exactly at their age level scored 100. That tradition stuck.
Later, psychologist David Wechsler switched to "deviation IQ," which compares you directly with people your age. He kept 100 as the average and chose 15 points as one standard step. Most modern tests still follow that pattern.
How test makers norm a test
"Norming" is the process that makes the average 100. Here's how it roughly works:
- Write the questions. Patterns, numbers, words, memory, logic.
- Pick a sample. Test makers give the test to a large group chosen to match the population by age, region, education and other factors.
- Score everyone. They record raw scores for each age band.
- Set the middle to 100. Whatever raw score sits in the middle of an age band becomes 100.
- Set the spread. They scale scores so that one standard deviation equals 15 points.
- Build the tables. Future test-takers get looked up against those tables.
So how is average IQ calculated? It isn't calculated from the world's population each year. It's fixed at 100 by the tables, based on the sample.
What this means for teens
Each age gets its own norms. That's why the average IQ of a teenager is 100 at 13, 15 and 17 alike.
Why tests get re-normed
Here's the twist. Over the 20th century, people kept doing better on IQ tests. Raw scores rose by roughly 3 points per decade in many countries. This is called the Flynn effect, after researcher James Flynn, who documented it.
So what happens if a test is normed in one decade and used 20 years later? People taking it later score above 100 on average, because they're being compared with an older, lower-scoring sample. The test becomes too easy.
The fix: re-norming. Test makers periodically collect a fresh sample and rebuild the tables. After that, the new average is 100 again.
Is average IQ dropping?
Some studies from Norway and a few other countries have found the Flynn effect slowing, stalling or even reversing in recent decades. Researchers still debate why. Either way, the published average on a current test stays 100, because re-norming resets it.
So "is average IQ going down?" has two answers:
- Raw performance may be rising in some places and flat or falling in others.
- The average IQ score on a freshly normed test is always 100.
Can a country's average not be 100?
Yes, and this is why you'll see "why is the average IQ not 100?" searches. If you give a test normed on one country to people in another country, their average can come out above or below 100.
But be careful with "average IQ by country" charts online:
- They often mix different tests, years and sample sizes.
- Some samples are tiny or not representative.
- Differences in schooling, health, language and test familiarity all affect results.
These charts are much shakier than they look, and they say nothing about any single person.
What "average" really covers
The average IQ meaning is simpler than people think: it's the middle score, not a description of a typical brain. And "average" covers a lot of ground.
| Range | Share of people (approx.) | Label on many tests |
|---|---|---|
| 90 to 109 | About 50% | Average |
| 85 to 115 | About 68% | Average range, broadly |
| 110 to 119 | About 16% | High average |
| 70 to 130 | About 95% | Everything but the far tails |
So is 110 IQ above average? Yes, a bit: it's around the 75th percentile, in the high average band. We break that down in is 110 IQ good for a 14 year old. And 100 on its own? See is 100 IQ good.
Average doesn't mean "same"
Two people at 100 can have very different skills. One might be sharp on words and slower on numbers; another might spot patterns fast but lose track of long problems. The average smooths all of that out.
Why the number matters less than the skills
Once you know the average is a set point, the score itself matters less. What you can actually change is the set of skills the questions test:
- Working memory: holding a few pieces of information while you use them
- Pattern spotting: seeing the rule in a sequence
- Mental arithmetic: handling numbers quickly and accurately
- Logic chains: following "if this, then that" steps without dropping one
- Putting reasoning into words: explaining why an answer is right
- Pace: not rushing, then not freezing
- Attention: staying on one problem
The hard part is knowing which of these is yours. Most people guess, and most guess wrong, because it's tough to watch your own thinking while you're busy doing it.
IQ Tester handles that part. It asks 16 questions about how you think, gives you a reasoning tier, and tells you which of those seven problems show up for you, so you train the right thing instead of guessing. Find my weak spots
A starter drill for each
- Memory: Chunk it. Group 9 digits into three sets of three.
- Patterns: Name the rule out loud before answering.
- Numbers: Estimate first, then calculate.
- Logic: write each link of the chain on its own line.
- Words: explain one answer in a single sentence.
See how you compare to 100, skill by skill
Why is average IQ 100? Because the scale is built that way, so the real question is what's behind your own score. In about two minutes, IQ Tester gives you a reasoning tier and your weak spots, then one tip and a 10-minute drill every day weighted toward them, with a streak and a history you can check anytime.
FAQ
Is average IQ always 100?
On a properly normed test, yes: the middle score of the norm group is set to 100. If the test is used on a different group or many years later, that group's average can drift above or below 100 until the test is re-normed.
Who decided average IQ is 100?
Early IQ tests used mental age divided by real age, times 100, so a typical child scored 100. When David Wechsler introduced the modern deviation IQ, he kept 100 as the average and set 15 points as one standard step.
Why do IQ tests get re-normed?
Because average performance changes over time. During the 20th century, raw scores rose about 3 points per decade in many countries (the Flynn effect), so old norms became too easy. Re-norming resets the average to 100.
Is average IQ dropping in 2026?
Some studies have found the rise in scores slowing or reversing in certain countries in recent decades, and researchers are still debating why. On any current, freshly normed test, the average is still 100 by design.
What is the average IQ of a normal person?
By definition it's 100 for their age group, and about two-thirds of people score between 85 and 115. "Normal" covers a wide range, and the score says little about any one person's strengths.