Mycroft Holmes IQ

Mycroft Holmes's IQ is estimated at 170 to 185. Sherlock Holmes himself says Mycroft has greater powers of observation than he does. Mycroft uses them to act as the British government's central brain, without leaving his armchair.

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Key facts

Estimated IQ: IQ 170 to IQ 185
Thinking style: Integrative and armchair
Known for: Being the smarter Holmes brother
Franchise: Arthur Conan Doyle stories, plus BBC Sherlock (2010 to 2017)
Compare with: Sherlock Holmes, James Moriarty, Near and Hannibal Lecter

Fan analysis for fun, reviewed September 2026. A fictional character cannot sit a real IQ test, so the range reflects what the character does in the story. How we estimate

Who is Mycroft Holmes?

Mycroft Holmes is Sherlock's older brother, seven years his senior. In the stories, Sherlock admits that Mycroft is the better observer and reasoner. What Mycroft lacks is energy: he will not chase a criminal across London when he could solve the case from his chair.

He spends his days between his rooms, his government office and the Diogenes Club, a club for men who do not want to talk to anyone.

The evidence: how smart is Mycroft?

01
The deduction duel
In The Greek Interpreter, Sherlock takes Watson to meet Mycroft. From the window of the Diogenes Club, the brothers study a stranger in the street and trade deductions: an old soldier, recently discharged, a non-commissioned officer in the artillery, a widower with children. Mycroft keeps pace with Sherlock and sometimes gets there first.
02
The British government
In The Bruce-Partington Plans, Sherlock reveals that Mycroft does not just work for the government. He is the one person who holds all the information from every department in his head, so ministers come to him to see how everything connects. At times, Sherlock says, he is the British government.
03
Keeping the secret
When Sherlock fakes his death at the Reichenbach Falls, the one person he trusts is Mycroft. In The Empty House, Sherlock reveals that Mycroft supplied him with money and kept his Baker Street rooms as they were during the years everyone else believed him dead.

How Mycroft thinks

Integrative and armchair. Mycroft thinks by connecting information from everywhere. He does not collect clues, he receives reports and sees how they fit together. He prefers not to test his conclusions in the field, which is why he hands the legwork to Sherlock.

Three strengths

Observation
He matches Sherlock deduction for deduction.
Integrating information
He holds the whole picture of the British state in his head.
Discretion
He keeps the biggest secrets in the stories, including his brother's survival.

Two blind spots

Inertia
He refuses to do fieldwork, so his conclusions often go untested until Sherlock checks them.
Withdrawal
He has built a life that requires almost no contact with other people.

Mycroft Holmes's personality type

Fans most often type Mycroft Holmes as INTJ. Fans usually type Mycroft Holmes as INTJ, in both the stories and BBC Sherlock. ISTJ comes up too, because of his rigid routine.

Big Five profile

Openness: High
Conscientiousness: High
Extraversion: Very low
Agreeableness: Low
Neuroticism: Low

Mycroft is methodical, private and unflappable, with a strong preference for routine. He is curious about systems more than adventures, and cool toward almost everyone except his brother.

Curious how your own Big Five compares with Mycroft's? Take the personality test.

Mycroft vs Sherlock Holmes, James Moriarty and Near

Character	Estimated IQ
Mycroft HolmesIntegrative and armchair	170 to 185
Sherlock HolmesDeductive, physical clues	155 to 175
James MoriartySystemic, hidden networks	165 to 185
NearPatient, methodical	138 to 158

Mycroft vs Sherlock Holmes
Sherlock says Mycroft is the sharper mind. Sherlock is the one who actually goes and proves it.
Mycroft vs James Moriarty
Both are the hidden brains behind vast networks. One serves the state; the other serves himself.
Mycroft vs Near
Two minds who solve cases from one room and send others into the field.

Mycroft vs Gottfried Wilhelm Leibniz

Leibniz was a polymath who served rulers as an adviser and librarian, trying to connect all human knowledge into one system. Mycroft's role as the government's living index of everything is a fictional version of that ambition.

Gottfried Leibniz's estimated IQ is 170+, a historical estimate from biographical records, not a test score. Read Gottfried Leibniz's IQ profile.

How we estimate fictional IQs

We look at what the character actually does: problems solved, plans that work, how fast they learn and how they compare with other brilliant characters in the same story. The range is a fan estimate, not a measurement.

Even the low end of the range, 170, would score higher than about 100.000% of people, roughly 1 in 652,598. Real tests become much less reliable this far above average.

Based on Doyle's The Greek Interpreter, The Bruce-Partington Plans and The Empty House.