This is useful and very smooth. Taking it for a test-run and as this is Show HN I'm not being picky, just some feedback.
On 'How much does it cost to hire?' https://mycompanyinfrance.fr/social-security
* I love that you can just choose one on the 4 input boxes and the others calculate. Lots of flexibility to let the user focus on what input they have and answer they want
* There's not an indication whether figures input are on a monthly basis, annual, or other. This affects the tax calculation: Entering 300, 3000, 30000 gets non-linear scaled results - major
* When re-clicking a field, previously entered digits need to be manually deleted rather than the field resetting - minor just my preference
* The breakdown of where contributions go lower down the page is great
* I'd input an existing French company that came to mind. Finding the 'This is not my company' link took a few minutes - minor
There is a fastidious amount of detail. You seem to have been very thorough e.g. bicycle allowance.
Does France also have tax, social insurance or benefit differences between cities/regions? Is it material? Is it worth the time/cost to manage?
On the reverse side, does France provide incentives regionally or based on city for starting companies?
For the above couple of questions, my context for asking:
I live in China and there's a lot of interest/very simple questions about tax that individuals and companies have. A handful of consultancies put online calculators for things like employment cost online and cover major cities (Beijing, Shanghai, Shenzhen, perhaps Hangzhou and similar) where social insurance contributions may vary.
They do this for free as a lead for their consultancy practices. They don't put calculators online for things like city- industry- specific incentives because this is a moving playing field with hundreds of cities moving incentive goalposts each month, it isn't practical to be accurate.
Are you looking for synergies with not only demystifying social security, but for example 'find an accountant' and 'find an office'. The potential for rabbit holes could be large, but also a very nice one-stop hosted CaaS (Company as a Service).