Legal - Assignment - Capital gain
The capital gain tax only applies if you are selling a secondary residence. There is no capital gains tax incurred if you sell your main home to buy another. The tax is applied to the difference between the sale price and that of the original purchase price plus the transaction costs - the gain.
The rate of Capital Gains Tax (CGT) for both French and non-French residents, who are residents of an EU country, is 19% of the net gain. If you are French resident you pay an extra tax 15.5% making the effective rate 34.5%.
If you are not an EU resident the rate goes up from 19% to 33.1/3%. This is subject to any applicable Double Tax Treaty.