If you go back to the basics it can be quite straightforward. And if you look at your online Ameli account it is quite detailed.
For every medical act, no matter how small, the seçu sets a price and then the percentage of that price it will normally pay. Which is somewhere between 0 and 100% (all set out on Ameli website if you wish to look at lists, here: Tableaux récapitulatifs des taux de remboursement | ameli.fr | Assuré)
The two complexities are firstly when the seçu price is way below the coats of that medical act. So for my insoles the seçu price is €27.50 per foot, and the normal reimbursement is 60% of that, or €16.50. Unfortunately the two insoles actually cost over €100, and the seçu will only pay €33 so I have to pay the rest myself.
If I had a 100% mutuelle they would then give me the missing 40% of the seçu set cost, so would top up to €27.50. So to get the costs completely reimbursed I would need to have a 200% mutuelle which would pay 200% of seçu set cost.
The second complexity is that no matter what your cover is there are also forfait and franchise for every act that are not reimbursed - often 50 centimes, but these can add up! Because so much is paid automatically I sometimes get taken by surprise when I’m expecting a big reimbursement and I get nothing as I have to pay off all the forfait and franchises first.
The next complexity is that some doctors are secteur 2, so are allowed to charge more than the seçu set cost for secteur 1. And this will not be reimbursed. Even in a public hospital some consultants do have “private” appointments where they are allowed to charge this (sometime sa useful way to get an earlier appointment for a very modest cost).
So as long as you know what the procedures are, what secteur they are in and then what percentage cover your mutuelle give for that type of thing you can work out the cost. Note that hospital procedures will have different element that are charged separately)
The final positive complexity is that some conditions give you the right to 100% reimbursement!
All opticians and dentists should now offer 100% santé options, which are modest costs. OH just had new glasses from his optician for 30€.