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Answer by Kynan Eng, tech startups and research, neuromorphic engineering:
It is not clear if Sherlock Holmes is rich, but he will need a decent after-tax income to live his lifestyle in modern London in 2016: 7,680 pounds ($10,064) per month living on his own or 5,460 pounds ($7,155) living with Watson. Before tax, he will need to make a rather hefty 12,828 pounds ($16,810) per month to live on his own or 8,346 pounds ($10,937) per month with Watson. We’ll assume that he doesn’t have any student loans or special tax exemptions.
Holmes does not seem to have many hobbies apart from his work and stimulating his intellect, and he does not seem to have any external financial commitments either. Hence it is relatively straightforward to estimate his expenses.
For rent, two-bedroom apartments in Baker Street go for around 3,300 pounds ($4,324) per month.
For housekeeping, it’s unclear what Mrs. Hudson charges for cleaning and minor catering duties, but housekeepers cost around 7 pounds to 10 pounds ($9-$13) per hour. Let’s say that she does 10 hours of work per week or 40 hours per month, for 400 pounds ($524) per month.
Holmes does not seem to use public transport very much. It’s unclear how much he uses taxis, but let’s say it is an average of twice per day—more when he is on a case, less between cases. This is 60 times per month, at any time of day or night. If we assume a moderate distance of a few miles for each trip at standard taxi fares of 25 pounds ($33) per trip, this works out to 1,500 pounds ($1,966) per month.
We will assume that Holmes is like Batman or Steve Jobs: He has just enough copies of the same or similar outfit to do his job. This website helpfully shows what clothes he wears: 1,350 pounds for his coat, 150 pounds to 460 pounds for his shirts, 495 pounds upward for his suits, 500 pounds for his shoes, and 308 pounds for his dressing gown. A fully stocked basic wardrobe might have two coats, 10 shirts, four suits, four pairs of shoes, and one dressing gown—a total of around 10,000 pounds ($13,105). Let’s say 12,000 pounds ($15,725) including socks, underwear, and other accessories. He will need to replace his entire wardrobe every five years, thus spending 2,400 pounds per year on clothing, or 200 pounds ($262) per month.
Holmes has highly developed senses and tastes and must therefore require high-quality food. Even if he never eats at restaurants, he will need at least 1,000 pounds ($1,310) per month to feed himself high-quality food and wine at home.
Total cost of the above when living on his own: 6,400 pounds ($8,387) per month. When he is sharing the rent and housekeeping costs with Watson, this comes down to 4,550 pounds ($5,963) per month. Adding 20 percent for incidentals, this comes to around 7,680 pounds living on his own or 5,460 pounds living with Watson.
Regarding incidental costs, Holmes is a known cocaine user. It is not clear how much he consumes, but given that U.K. cocaine prices appear to be around 54 pounds ($71) per gram (around two taxi trips), I’m going to assume that this falls into his 20 percent incidentals. His other known habit of violin playing is not expensive in terms of running costs.
The median person living in London earns around 4,000 pounds ($5,241) per month. Whichever way you look at it, Sherlock Holmes needs to be making a lot of money to be a private detective.
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