* You only have the basic, state social security (the 17% part OP talks about). This basically only covers you for emergency situations. There's tons to pay out of pocket in case of pretty much anything (hospital stays, glasses, teeth work, etc). This is usually covered by a complementary insurance, usually paid for by the employer (mutuelle). Private people can subscribe to it, but it costs extra.
* You do not contribute to any retirement. If you only do this for your whole life, at the end, you will only get the absolute minimum retirement (which is ridiculous).
* You do not get unemployment in case your business fails.
* In case of accident that prevents you from working (say car crash and you end up paralyzed or something) you're SoL. A "regular employee" (especially engineer level) could have an insurance covering this. In the situation described here, you'd have to pay extra or not get any money anymore.
All this is to say that for all the taxes paid (almost 50% !) you get pretty much... nothing. I'm curious how this compares to other countries with lower taxes where you're expected to pay for insurance out of pocket.
There's also another fun fact: once you have your 50k in hand after having paid the other 50k to the state, it doesn't stop there! Want to go buy something? The state would love you to, they get 20% out of that too!
I'd be curious to see a similar breakdown for the US in particular, where people usually say that for the higher salaries you have to pay more for healthcare. Maybe the extra insurance is much more expensive over there, don't know.
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Parent's error is you don't count the VAT in the revenue. It's invoiced on top of it and it goes back to the state directly. Also, if you have 100K in yearly revenue, it's not a good deal to pay regular income tax on that, the 30% flat rate is more advantageous.
All in all, your 100% dividend works out to 53869 which is a roughly 5% increase over their estimate.