A doubt that often plagues the mind by the time you are nearing the financial year end is what is the tax you have to pay and where.
Though your colleagues and the institute office will help you with this, these are a few points you might be interested in knowing:
1- Find a document on French Tax System here.
2- Unlike in India, the salary is divided by the number of dependents – so that if you have a spouse who is not working, or children, your tax liability will be less.
3- The place you live in is also a deciding factor in tax calculation.
You need to get a form of tax declaration from the office (the tax people come to the institute during this period and are quite helpful) and fill the details and post it. Then you will get a reply after a few weeks, regarding how much you have to pay and in case your salary is not too high, you might end up getting some money back from the government!
Since postdoc salaries are rarely very high, income tax is not a big concern while choosing a position in France.
The website for income tax is this.

