Taxes — Progressive IR and prélèvement à la source

French personal income tax is built around the progressive IR (impôt sur le revenu), with PAS (prélèvement à la source, withholding at source) introduced in 2019, so tax is deducted month by month from wages, pensions, and estimated self-employed earnings. From a Korean perspective, this is closer to "monthly withholding plus a return the following year" than to Korea's year-end adjustment. Separately, social-purpose levies — CSG (Contribution sociale généralisée) and CRDS — apply to wages, pensions, and capital income, so looking only at IR misses a meaningful part of the burden when comparing take-home pay.

Core concepts:

• Tax residence (résidence fiscale) — usually judged on a combination of factors: principal residence, centre of personal interests, more than 183 days in France, or principal economic activity. Residents are taxed on worldwide income; non-residents are taxed mainly on French-source income.
• Progressive rates with parts (household-based calculation) — France files at the household (foyer fiscal) level, dividing taxable income by quotient familial (the number of parts in the household) before applying the rates and aggregating again. The more children, the lower the effective rate (subject to a plafonnement cap).
• PAS (withholding at source) — wages and pensions are withheld monthly by the employer or pension institution; for the self-employed and rental income, monthly or quarterly acomptes are taken. A return (déclaration de revenus) the following spring reconciles the year.
• CSG/CRDS — social-purpose levies on wages, replacement income, and capital income. Part is deductible against IR and part is not.
• Capital income — generally taxed under a single flat tax (PFU, "flat tax" 30% — including the IR portion and social levies), with the option to elect into the progressive scale. Real estate, foreign accounts, and crypto-assets carry separate reporting obligations.
• Property and local taxes — Taxe foncière for property owners, Taxe d'habitation (largely phased out for principal residences and now mainly applies to secondary homes), and IFI (Impôt sur la fortune immobilière) real-estate wealth tax may apply separately.

Particularly important for people coming from Korea:

• Korea–France tax treaty (signed 1979; a new treaty is set to apply from December 2025) — sets rules for residence determination, foreign tax credits, and the allocation of taxing rights on employment income, pensions, dividends, interest, and royalties. Determining the treaty country of residence is the key to avoiding double taxation.
• A déclaration de revenus is mandatory from the first year for residents. For your first return, after obtaining a tax identification number (numéro fiscal), you can file by paper (Form 2042 or similar) or via impots.gouv.fr.
• Foreign accounts and assets — Korean and other foreign bank accounts must be reported each year. Penalties for non-disclosure are significant.
• Change of nationality, return home, pension receipt — when receiving a French pension after returning to Korea (or vice versa), confirm in advance which country has the taxing right under the treaty to keep withholding and refunds smooth.
• First-year effect — in your arrival year, income is split between the pre- and post-residency periods; on departure, the timing of the non-resident transition and the suspension of PAS need to be handled.

Official guidance: impots.gouv.fr, service-public.fr — impôts, urssaf.fr