If you live in France but work in the UK — a "frontier worker" — and are paid via PAYE, declaring your income correctly is essential to benefit from the tax credits provided by the France-UK Double Tax Agreement. Get this right and French tax on your UK salary is neutralised. Get it wrong and you may end up paying French income tax on earnings that were never meant to be taxed there. This guide explains exactly how to calculate your taxable figure and which boxes to use on Forms 2047 and 2042. For a full overview of the filing process, see our complete guide to filing French taxes as a UK expat.
The Core Legal Requirement: As a tax resident of France, you are legally required to report your worldwide income. According to the official instructions for Form 2047: "You must fill in a declaration no 2047 if your household received income outside metropolitan France... You must obligatorily report the amounts entered on your 2047 in the corresponding sections of your main declaration (no 2042, 2042C or 2042C Pro)."
Step 1 — Calculate Your Net Imposable Figure
The most common mistake is using the wrong starting figure. France requires you to report the Net Imposable amount — not your take-home pay, but not your absolute gross either. It is your gross salary minus specific mandatory deductions.
What to Deduct
Under the French General Tax Code (CGI, art. 83), salaries must be declared after deduction of mandatory social security contributions and contributions paid to mandatory retirement or providence schemes. For UK PAYE workers this means:
- UK National Insurance (NI): Deduct your mandatory employee NI contributions.
- Mandatory Pension: Deduct contributions made to mandatory schemes, including those under UK auto-enrolment. Voluntary contributions (AVCs) are generally not deductible.
What NOT to Deduct
- UK Income Tax (PAYE): You must report the amount before UK tax was deducted. The official instructions state: "When reporting income that opens a right to a French tax credit, you must declare the amount without deduction of the tax paid abroad."
- French 10% Professional Allowance: Do not apply this yourself. The tax office applies the 10% deduction automatically to the figure you provide.
Summary Formula:
Net Imposable = UK Gross Salary − Mandatory Employee NI − Mandatory Pension Contributions
This is the single figure you will use in every box and section below. When converting GBP to euros, always round every figure to the nearest whole euro.
Currency conversion across a full year of UK employment is one of the more time-consuming parts of preparation. Taxpert's basic tool handles this automatically — it applies the correct annual exchange rates, calculates your Net Imposable, and produces a filing-ready summary for both Form 2047 and Form 2042.
Step 2 — Form 2047: Declaring the Foreign Income
Form 2047 is the dedicated annex for foreign-source income. It must be completed before your main return, as figures flow from it into Form 2042.
Form 2047 — Section 1, Line 10
- Enter your Net Imposable figure.
- In the Nature field, describe the income as "UK Salary".
- Tick the "Privé" box — unless you are employed directly by a UK government body (e.g. a civil servant or teacher employed by a public authority), in which case different treaty rules may apply.
Form 2047 — Section 6 (Double Tax Neutralisation)
This is the most critical step to ensure you are not taxed twice. You must report the same Net Imposable figure here again. The form states this section is for "income taxable in France which, by virtue of an international tax convention, opens a right to a tax credit representative of the foreign tax."
Completing Section 6 is what instructs the French system that a tax credit must be generated against this income. Omitting it means the credit is never created — and you will face a French tax bill on UK income.
Step 3 — Form 2042: The Main Return
Form 2042 — Section 1 (Salaries): Box 1AF or 1BF
- Transfer your individual Net Imposable total to Box 1AF (Declarant 1) or Box 1BF (Declarant 2).
- If both spouses or PACS partners work in the UK as frontier workers, each person's figure goes in their respective box.
Form 2042 — Section 8 (Tax Credits): Box 8TK
- Enter the total household amount — both declarants' combined Net Imposable — in Box 8TK.
- This box is the mechanism that "triggers a French tax credit that neutralizes the French tax" on this specific income. Without it, the credit is not applied even if Section 6 of Form 2047 was completed.
Why both Section 6 and Box 8TK? Section 6 on Form 2047 identifies the type of income eligible for a credit. Box 8TK on Form 2042 is the claim for that credit on the main return. Both are required. One without the other leaves the mechanism incomplete.
Quick Reference: Frontier Worker Box Summary
| Form | Section / Box | What to Enter | Purpose |
|---|---|---|---|
| 2047 | Section 1, Line 10 | Net Imposable (per declarant). Nature: "UK Salary". Tick Privé. | Declares the foreign employment income |
| 2047 | Section 6 | Same Net Imposable figure | Identifies income as eligible for double tax credit |
| 2042 | Box 1AF / 1BF | Individual Net Imposable total | Reports salary on main return |
| 2042 | Box 8TK | Combined household Net Imposable total | Claims the French tax credit — eliminates French income tax on the UK salary |
Important Caveats for Frontier Workers
Social Charges Are Also Neutralised
UK employment income for frontier workers is typically subject to a tax credit that neutralises French social charges as well as income tax. Social charges (CSG/CRDS) are not applied to this income type via the tax credit mechanism — meaning the double tax relief covers the full French tax exposure on your UK salary, not just the income tax portion.
Currency Conversion
When converting your GBP income to euros, always round every figure to the nearest whole euro. For recurring annual salary income, using the year-average exchange rate for 2025 is permitted. Taxpert's basic tool applies the correct rate automatically and shows the converted figure ready to enter into each box.
Record Keeping
You do not need to attach your payslips or P60 to the return. However, you must retain all supporting documents — payslips, P60, pension statements — for at least three calendar years following the year of payment, in case of an audit.
If You Have Filed Without Box 8TK in Previous Years
This is one of the most commonly reported errors among frontier workers. If you have filed returns in prior years declaring your UK salary on Form 2047 but did not complete Box 8TK, you may have overpaid French tax. The DGFiP correction window (typically open in late July each year) allows you to amend previously filed returns. You can also file a formal réclamation (claim) for refund of overpaid tax, generally within the two-year window following the year the tax was paid.
Where This Fits in Your Full Declaration
Frontier worker salary is one income type within what is often a broader UK-source picture. Many frontier workers also have UK savings interest, dividends, or pension income to declare. Each income type has different treaty treatment, different sections on Form 2047, and different boxes on Form 2042. For the full map of every UK income type and where it goes, see our complete guide to filing French taxes as a UK expat.
Pro Tip: In the online impots.gouv.fr portal, you often cannot fully complete the 2042 main return before the 2047 annex. Navigate to the 2047 annex first, complete Sections 1 and 6 for your UK salary, then return to the main 2042. Some income types will auto-populate from 2047 — but Box 8TK must always be completed manually.