I've worked several years in in London, Paris and now the Northeastern USA, so I think I am in a position to draw some high-level conclusions. In a word, your friend is not wrong about there being hidden costs in the US. However, for many high-education jobs, American employers pay significantly more. In pure monetary terms, a software developer will be much better off in the US.

I think it's really hard to have this discussion without some hard numbers. Note that this is a simplified analysis. I am not accounting for the various deductibles (social security, etc.), state taxes etc. I have restricted the analysis to roughly-comparable cities, but it seems to hold at the national level as well.

Currency conversions are left as an exercise to the reader :)

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Median salary for a senior developer

- Paris: 65k € (Paris) (n.b.: some sources say 45k €, but this does not match my experience)

- London: 90k £

- New York City: $160k

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Tax Brackets in France

Up to 10,225 € 0 %

From 10,226 € to 26,070 € 11 %

From 26,071 € to 74,545 € 30 %

From 74 546 € to 160,336 € 41 %

Above 160,336 € 45 %

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Tax Brackets in the United Kingdom

Up to £12,570 0%

From £12,571 to £50,270 20%

From £50,271 to £150,000 40%

Above £150,000 45%

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Tax Brackets in the United States

From $0 to $9,950 10%

From $9,951 to $40,525 $995 plus 12% of the amount over $9,950

From $40,526 to $86,375 $4,664 plus 22% of the amount over $40,525

From $86,376 to $164,925 $14,751 plus 24% of the amount over $86,375

From $164,926 to $209,425 $33,603 plus 32% of the amount over $164,925

From $209,426 to $523,600 $47,843 plus 35% of the amount over $209,425

Above $523,600.99 $157,804.25 plus 37% of the amount over $523,600

There are many reasons to pick one place to live over another, but it's very difficult to argue against the enormous economic advantage to working in the US, even with the "hidden costs".

With regards to health insurance in particular, it's important to point out that the quality of care on the upper end of the spectrum is far better than anything I've ever had access to in Europe. I pay $1.2k/month in health insurance and pay nothing out of pocket for: dental, vision, emergency care, ambulance transportation, extended stay in hospital, mental health services, etc. I have a $10 copay for all medications. Waiting times for appointments are on the order of single-digit days. If you make the median income for a senior software dev in NYC, that leaves you with about $145k.

Concerning cars, they are far more affordable here than in Europe, especially if you buy a reliable used car. I drive a 2000 Subaru Legacy with about 125k miles on it. It costs me about $850/year to insure. I pay about $100/month in gas, so let's round that up to $1,500 per annum. Last year, I spent $1,236.57 in maintenance & repairs. Total cost of ownership: approximately $3,600 per annum. If you make the median income for a senior software dev in NYC, that now leaves you with $141,400.

College education? It's wildly variable, but let's take the pessimistic case of sending your two children to an Ivy League school that costs $75k per year. Let's be even more conservative and factor in an additional $25k in non-tuition costs (room & board, meals, books, pocket money, etc.). That's a total of $800k for two BAs. Assuming you have twins who go to college at the same time, that leaves you with 18 years to accrue those savings, or about $45k/year. Taking the leftover salary, that leaves you with about $96k. For comparison, my education in an American "public Ivy" school cost about 36% of this figure, which would leave you with about $125 in gross annual income. There are tax deductions for tuition fees, and many scholarships available for good students.

It bears repeating that there are many good reasons to prefer living in Europe over the US. Economic analysis is not the only relevant analysis. But, it is very difficult to argue that the cost-of-living breaks even for the overwhelming majority of STEM jobs, or jobs requiring post-secondary education. If you have a college degree, you will almost certainly have more money in the United States than in the European Union, by a significant margin. There is a reason the Brain Drain exists.