[1] : https://www.service-public.fr/particuliers/vosdroits/F1419 [2] : https://www.insee.fr/fr/statistiques/serie/010752333 [3] : https://www.insee.fr/fr/statistiques/6436313#titre-bloc-9
If you look at income tax in high income tax states the income tax looks similar, so its the payroll taxes and VAT that really is the difference between France and US.
You'll hear "I win 100k a year", not "I win 181k a year". During hiring, you negotiate on the 100k number. Your contract mention this number. In the end, if there is a tax raise on the company part, they have to maintain your salary to the same level, even if it ends up costing them more than before.
That'd be also why US salaries seem so high from the outside, but are less impressive once your factor this in.
Sadly, US salaries don’t just seem much higher than Europe: they are much higher. Take home pay after all taxes for a senior engineer at a large public tech company can commonly be $250k+ per year, in addition to benefits like health insurance and 6+ weeks off once vacation and holidays are taken into account.
Income tax in France is progressive. You slice your income in brackets, and for each there's a tax rate. Your average tax rate is the average of your brackets.
The highest bracket in France is 45% for income above 160k, so for your total income tax rate to be about 40%, it would mean that you make an absolute shitload of money.
Income tax brackets, French, but the table is clear enough: https://www.service-public.fr/particuliers/vosdroits/F1419