Before you start

A French tax number, issued after your first declaration
Records of worldwide income for the year
A French bank RIB
Credentials for impots.gouv.fr

Step-by-step

1
Understand that withholding does not replace the declaration
Prélèvement à la source deducts tax from your salary, but the annual declaration in the spring is still mandatory. It reconciles the withholding, applies the household quotient and reliefs, and captures income the withholding never saw.
OnlineWho: YouSpring annually
2
File your first declaration on paper if you have no tax number yet
The online service needs a tax number you do not have until you have filed once, so the first declaration usually goes on paper to your local tax office. This circularity catches everybody and the office is used to it.
In personWho: You
3
Work out your parts and what the quotient does for you
A single person is one part, a married or PACSed couple two, with additional half-parts for children. Income is divided by the parts, taxed on the scale and multiplied back — a substantial reduction for couples with unequal incomes and for families.
OnlineWho: You
4
Establish your residence position for the year of arrival
France taxes residents on worldwide income. The year of arrival is usually split, with foreign income before the move treated separately, but the rules and any treaty with your previous country matter. Take advice on the first declaration if you have income from both sides of the move.
In personWho: You
5
Declare foreign accounts — the penalty is real
French tax residents must declare all foreign bank accounts, life insurance policies and digital asset accounts annually, whether or not they generated income. The fixed penalty per undeclared account is significant and it is applied.
OnlineWho: You
6
Check the position on any second home you keep
There is no residence tax on your principal home, but second homes are still taxed and communes in pressured areas can apply substantial surcharges. Much of the Gironde coast falls into that category. If you are keeping or buying a place at Arcachon or on the coast, check the local rate rather than assuming.
OnlineWho: You

Documents you’ll need

French tax number, once issued
Salary statements and the annual employer summary
Records of all foreign income and foreign accounts
RIB for refunds and payments
Marriage or PACS documentation, for household parts

Things most newcomers don’t know

France taxes the household, and that changes the answer completely depending on who you are.

The quotient familial divides household income by a number of parts before applying the scale. A couple with one high and one low income pays substantially less than two individuals earning the same amounts would; a single high earner does comparatively badly. Any comparison of French tax against a country with individual taxation is meaningless without specifying the household.

Source: impots.gouv.fr

Second-home surcharges on the Gironde coast are real and rising.

Taxe d'habitation was abolished on principal residences but retained on second homes, and communes classified as being in pressured housing areas may apply substantial surcharges on top. Much of the Atlantic coast around Arcachon and the Bassin qualifies, precisely because holiday homes there displaced local housing. Anyone buying a weekend place should check the specific commune's rate before, not after.

Source: service-public.fr

You must still file, and the first one is usually on paper.

Withholding at source is not the end of the obligation, and the online service requires a tax number you only receive after filing once. Newcomers assume that since tax is being deducted there is nothing to do, then find themselves reconstructing a missed declaration a year later.

Source: impots.gouv.fr

Undeclared foreign accounts carry a fixed penalty per account, per year.

French tax residents must list every foreign bank account, life insurance contract and digital asset account annually, regardless of whether it earned anything. The penalty is a fixed amount per undeclared account and it is applied rather than theoretical. A dormant account in your home country is exactly what triggers it.

Source: impots.gouv.fr

Common mistakes to avoid

Assuming withholding at source removes the obligation to file annually.
Not realising the first declaration goes on paper because you have no tax number yet.
Failing to declare a dormant foreign bank account and incurring the fixed per-account penalty.
Buying a second home on the coast without checking the commune's surcharge.
Comparing French and foreign tax rates without accounting for household quotient parts.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.