The flat tax
Net gains are taxed at the prélèvement forfaitaire unique, made of 12.8% income tax plus social charges, about 30% in total. Social charges on capital income have been changing, so check the current rate for your tax year. You can opt for the progressive income tax scale instead.
How gains are calculated
France uses a whole portfolio method: each taxable sale is compared with the total acquisition cost and the total value of your crypto holdings at that moment. Disposals totaling €305 or less in a year are exempt.
Staking, mining and professional trading
Mining and frequent professional trading can be treated as business income with different rates and social charges. The treatment of staking rewards is not fully settled; many advisers treat them as non commercial income when received. Ask a professional for your case.
Reporting
Declare gains on form 2086 and carry them to form 2042 C. Every account held on a platform abroad must be declared on form 3916 bis, even with no sale; failing to do so carries fines.