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, once you have a number

Step-by-step

1
Fix the withholding rate on your first payslips
With no French tax history, your employer applies the taux neutre from a published grid based on your salary alone. It ignores your household, your children and any other income. Once you have a tax number you can request a personalised rate through impots.gouv.fr, and you can modulate it when your circumstances change. Do this rather than waiting a year for the reconciliation.
OnlineWho: YouAs soon as you have a tax number
2
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
3
File your first declaration on paper if you have no tax number yet
The online service needs a tax number you do not receive until you have filed once, so the first declaration usually goes on paper to your local tax office. This circularity catches everyone and the office is entirely used to it — ask them directly.
In personWho: You
4
Work out your parts and what the quotient does for your household
A single person counts as one part, a married or PACSed couple as two, with additional half-parts for children. Income is divided by the parts, taxed on the scale and multiplied back. The reduction is substantial for a couple with unequal incomes and for families.
OnlineWho: You
5
If you commute to Paris, work out what is actually deductible
France gives every employee a standard 10% deduction for professional expenses, but you may instead deduct real costs — frais réels — including commuting, and for a Rouen-to-Paris season ticket that can be worth substantially more than the flat allowance. The choice is made in the declaration and applies to the whole household member's income, so it needs a calculation rather than a guess. Keep the tickets and the employer's contribution statement.
OnlineWho: You
6
Declare every foreign account — the penalty is fixed and it is applied
French tax residents must list all foreign bank accounts, life insurance contracts and digital asset accounts annually, whether or not they generated income. The account people forget is almost always a dormant one at home.
OnlineWho: You

Documents you’ll need

French tax number, once issued
Payslips and the annual employer summary
Season tickets and travel receipts, if you claim real expenses
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

If you commute to Paris, the frais réels option is the most valuable line in your declaration.

Every French employee gets an automatic 10% deduction for professional expenses. Anyone can instead elect to deduct actual costs, and a Rouen–Paris rail season ticket net of the employer's mandatory contribution is a large enough number that it often beats the flat allowance comfortably. It is elected in the declaration, it requires you to have kept the evidence, and it is the single most commonly missed thing by people who take the train to the capital.

Source: impots.gouv.fr

The rate on your first French payslip is a guess, and you can correct it in ten minutes.

With no filing history, prélèvement à la source falls back to the taux neutre — a published grid keyed to salary alone that knows nothing about your spouse, your children or your other income. For a single earner supporting a family it is usually far too high; for two earners it can be too low, storing up a bill. Once you have a tax number you can request a personalised rate online and it applies within a couple of months. Most newcomers never realise the number was provisional.

Source: impots.gouv.fr

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

The quotient familial divides household income by a number of parts before applying the scale — one for a single person, two for a married or PACSed couple, extra half-parts for children. A couple with one high and one low income pays substantially less than two individuals earning the same amounts; a single high earner does comparatively badly. Comparing French tax against a country with individual taxation is meaningless without specifying the household.

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 on a dedicated form, regardless of whether it earned anything. The penalty is a fixed amount per undeclared account, higher where the account sits in a state with no anti-fraud agreement with France, and it is applied rather than theoretical. The one people forget is a dormant current account in their country of origin.

Source: impots.gouv.fr

Common mistakes to avoid

Taking the automatic 10% deduction when a Paris season ticket would make frais réels worth more.
Accepting the taux neutre on your payslip as though it were your actual tax rate.
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.

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