- If you paid social charges on pension income last year, part of what you paid is deductible against this year's income tax — but only if you apply it yourself
- For investment income, this deduction auto-fills into Box 6DE most of the time. For pension income, there is no equivalent box at all — it has to be calculated manually and folded into the gross figure you declare
- The deductible portion is 3.8 points if your pension is in the reduced social charges band, or 5.9 points if it's in the standard band — the rest isn't deductible
- Missing this doesn't trigger an error or a query from the tax office. Nothing on the return tells you it's missing — you simply pay income tax on money that shouldn't be taxable
Ask most UK pensioners in France whether they've ever heard of the CSG déductible and you'll get a blank look. That's not because it's obscure — it's a genuine, government-sanctioned reduction to your taxable income — it's because for pension income specifically, there's nothing on the return that reminds you it exists.
This is a different topic from the S1 exemption itself. This deduction only applies if you don't hold an S1 and are therefore paying social charges on your pension income. If you're not sure whether you should be paying social charges, check out How to Stop Paying Social Charges on Your UK Pension in France first — this article assumes you already know the answer is yes, for this year or a prior one. For the full picture of how UK private pension income is taxed and declared in France, see UK Private Pension in France: Tax, Declaration and the Treaty Rules, which this article builds directly on. For the wider picture of how French tax works for UK expats generally, see How the French Tax System Works.
What the CSG Déductible Actually Is
CSG (Contribution Sociale Généralisée) is the largest component of the social charges you pay on pension income if you don't hold an S1. Part of what you pay is, itself, deductible against your income tax the following year — a genuine reduction, confirmed on your Avis d'Impôt, not a workaround or a grey area.
How much is deductible depends on which social charges band you're in:
| Your social charges band | Total rate | CSG portion | Deductible portion |
|---|---|---|---|
| Reduced | 4.3% | 3.8% | 3.8 points — fully deductible |
| Median | 7.4% | 6.6% | 4.2 points deductible, 2.4 not |
| Standard | 9.1% | 8.3% | 5.9 points deductible, 2.4 not |
See "How to Actually Apply It" below for exactly how this deductible figure gets used on your return.
For the full breakdown of the social charges bands themselves and how your rate is determined, see Revenu Fiscal de Référence: The One Number That Controls Your Benefits.
Why Investment Income Gets a Box and Pension Income Doesn't
Form 2042 has a dedicated line — Box 6DE, under "Charges déductibles" — labelled explicitly "CSG déductible, calculée sur les revenus du patrimoine" (CSG deductible, calculated on wealth/investment income). For income like dividends, interest, and rental income, this box is often pre-filled by the tax office directly from your previous year's Avis d'Impôt.
Pension income has no equivalent box. There is no line on Form 2042 labelled "CSG déductible sur pension." The mechanism for applying it is completely different: you have to work out the deductible figure yourself and subtract it from your gross pension amount before you enter that figure into Box 1AM or 1BM.
Nothing on the return prompts you to do this. Often declarers simply enter the full gross pension amount without knowing that they were overpaying income tax.
How to Actually Apply It
Step 1 — Find the figure. On your previous year's Avis d'Impôt, look for a line labelled CSG déductible in the social charges section. This shows the deductible amount from what you paid last year.
Step 2 — Calculate your reduced gross figure. Subtract that CSG déductible figure from this year's gross pension income.
Step 3 — Use the reduced figure in the right place. Enter the reduced amount in Box 1AM (Declarant 1) or Box 1BM (Declarant 2) on Form 2042, and on Line 12 of Form 2047.
Critical: don't use the reduced figure everywhere. The social charges are calculated on the gross pension income — Form 2042 C, and Section 9 of Form 2047 if you're a non-S1 holder, still require the full gross figure, not the reduced one. Mixing these up in either direction either overpays income tax or underdeclares social charges. The reduced figure is for income tax purposes only.
Working out which figure goes where — the reduced amount for Box 1AM/1BM, the full gross amount for the social charges boxes — is exactly the kind of multi-step, easy-to-mix-up calculation Taxpert's filing assistant is built to walk you through, box by box.
Why This Is Easy to Miss Every Single Year
Unlike the investment-income version, which the tax office often pre-fills for you, the pension version requires you to actively go back to a previous document, do a subtraction, and remember which box gets which figure. Miss it once, and there's no natural correction point the following year — you simply repeat the same overpayment, indefinitely, because nothing on the return ever flags that a figure is missing.
This is also easy to conflate with the investment-income mechanism, since both share the name "CSG déductible" and the same underlying logic — but they are declared in structurally different ways, on different lines, for different income categories. Fixing one doesn't fix the other.
Common Mistakes
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Assuming this works the same way as the investment-income version. Box 6DE is for patrimoine income and is often pre-filled. There is no equivalent box for pension income — it has to be applied manually to the figure itself.
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Not checking the prior year's Avis d'Impôt for the CSG déductible figure. If you don't go back and find it, there's nothing prompting you to look. It's easy to file year after year without ever applying this.
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Using the reduced figure in the social charges declaration too. The reduced figure belongs only in Box 1AM/1BM (income tax) and Line 12 of Form 2047. Form 2042 C and Form 2047 Section 9 need the full gross amount.
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Assuming a current S1 rules this out entirely. The deduction itself only ever comes from a year you paid social charges — but if you paid social charges on pension income in a prior year, before your S1 was registered, that year's CSG déductible figure is still real and still usable now, even though you're an S1 holder today.
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Not realising the deduction only applies to the year after you paid. The CSG déductible you claim this year is based on what you paid last year, not what you're paying now. There's always a one-year lag.
Frequently Asked Questions
What is the CSG déductible on pension income?
A portion of the social charges (specifically CSG) you paid on pension income last year that's deductible against this year's taxable pension income. The deductible portion is 3.8 points at the reduced band, 4.2 points at the median band, or 5.9 points at the standard band — the remainder (CRDS, CASA, and part of the CSG at higher bands) isn't deductible.
Why doesn't my pre-filled tax return include this automatically?
Unlike investment income, which has a dedicated box (6DE) the tax office often pre-fills, pension income has no equivalent box. The deduction has to be applied manually by reducing the gross pension figure you enter — there's nothing that prompts or auto-calculates it for you.
Which box do I put the reduced figure in?
Box 1AM (Declarant 1) or Box 1BM (Declarant 2) on Form 2042, and Line 12 of Form 2047. Do not use the reduced figure anywhere else — the social charges declaration itself (Form 2042 C, and Form 2047 Section 9 for non-S1 holders) needs the full gross amount.
Does this apply if I hold an S1?
The deduction itself is only ever generated by a year you paid social charges, which means it doesn't apply to a current S1 holder's current pension income. But if you paid social charges on pension income in a prior year — for example, before your S1 was registered, or during a gap year — that prior year's figure is still usable now, even though you're an S1 holder today.
Where do I find the figure to use?
On your previous year's Avis d'Impôt, in the social charges section, look for a line labelled CSG déductible. That figure is what you subtract from this year's gross pension income.
What happens if I've been missing this for years?
You've likely been overpaying income tax slightly each year without realising it. Unlike a missed S1 declaration, this doesn't carry the same reclaim mechanism discussed elsewhere on this site — check with your tax office or an accountant about whether a correction is possible for prior years, and make sure to apply it correctly going forward.
Sources: Official Form 2042 (Cerfa n°10330*29, "Déclaration des revenus," Section 6 "Charges déductibles" — direct read of the real form, confirming Box 6DE is explicitly scoped to "CSG déductible, calculée sur les revenus du patrimoine," with no equivalent box present anywhere in Section 1 for pension income) · CSG déductible en 2026: comment ça marche? (confirms the deductible-points breakdown by band: 3.8 at the reduced rate, 4.2 of 6.6 at the median rate, 5.9 of 8.3 at the standard rate) · uk-private-pension-taxed-in-france.md and reduce-french-tax-bill-strategies.md (this project's own verified figures for the pension-income and investment-income mechanisms respectively, reused here without re-deriving)