There is no way to calculate for sure an 'exact' figure.
May seem crazy, but welcome to France. The authorities 'guestimate' as much as the citizens do for the simple fact that all the myriad of deductions are so complex and interconnected that it is a nightmare.
How do I know this for a FACT?
Simple, had a tax investigation and review a few years ago....6 months under review and then a 3 month extension with full open book review by the tax and social security investigators.
The result.....my annual tax declarations were deemed absolutely 100% accurate...and correct.
This was a tad of a surprise to me as I had guessed them in the first place as best approximations. Having given up trying to understand the 'system'....and work out every single line item. So my declarations were 100% correct. Great.
Then, I was fined a massive 50 Euros because I had underpaid my social charges. The only thing was that I had paid EXACTLY the social charges requested of me by the State based on their calculations from my declarations, which recall were deemed correct. So effectively they were saying their own previous calculations were incorrect...not my payments.
Ipso facto......They guess.......
So it's a lottery what you pay......and likely having some well placed 'friends' is more use in determining what amount of tax you pay, than any amount of detailed calculation.
This isn't actually corruption....it's just rank inefficiency and massive overcomplication making this the only way anything can function at all.
Last edited by HyFlyer; 1st Feb 2018 at 00:21.