Remember it's household income:
Whereas in the UK you pay tax as an individual, in France you are taxed by household. So if you are a married couple or if you are “pacsed” (in a civil partnership) then you should make one joint declaration rather than two. If you got married half way through the year you can now declare one common declaration (instead of three, which was previously the case) for the whole year.
And if you have any children living with you that are earning then you’ll need to declare their earnings too.