- If only one partner in a couple holds an S1, the reduced 7.5% solidarity levy applies only to that partner's share of joint income — not automatically to the whole household
- The default split is 50/50 for jointly held income, but it should reflect the actual ownership split if that's different — for example, an account held 70/30
- Form 2042-C has a dedicated block for exactly this situation: it explicitly states "fill in the boxes below only if you are married or PACS'd and only one of the two spouses meets the S1 condition." The boxes are 8RF (rental income), 8RV (purchased life annuities), 8RC (dividends and interest), and 8RM (securities capital gains) — one box per income category, each holding the S1 holder's isolated euro share
- Skip this declaration and the tax office has no way to know only one of you qualifies — it will default to charging the full rate on the entire joint amount
A couple splitting a joint investment account 50/50 assumed their S1 automatically covered half their social charges bill, because only one of them held the certificate. It doesn't work like that. Unless the S1 holder's share is specifically isolated on the return, the tax office has no way to apply the reduced rate to only part of a joint income figure — and depending on how the return is filed, either the whole amount gets the full rate, or the whole amount gets treated as if both partners qualified. Neither is correct, and neither happens automatically in your favour.
If neither of you holds an S1, this article isn't for you — see No S1 and Living in France? instead. If you're not sure what an S1 does or whether you qualify for one at all, start with How to Stop Paying Social Charges on Your UK Pension in France, which covers the certificate itself and the single-holder mechanics this article builds on.
Why a Joint S1 Situation Doesn't Work Like a Single One
When both partners hold an S1, or neither does, the household's social charges rate is uniform — there's one rate, applied to everything. Ticking Box 8SH (or 8SI for a second declarant) on Form 2042-C tells the tax office your entire relevant income qualifies for the reduction.
A mixed household — one S1 holder, one not — breaks that simplicity. France still assesses your household as a single fiscal unit (foyer fiscal) for most purposes, but social charges specifically need to track which portion of income actually belongs to the exempt partner. The tax office cannot infer this on its own from a joint income figure. You have to state it.
For the foundational explanation of how households and shared income work in French tax generally, see How the French Tax System Works.
Working Out the S1 Holder's Share
For jointly held income covered by the four boxes below — a shared investment account, jointly owned rental property — the starting assumption is a 50/50 split between partners.
That's a default, not a rule. If ownership is genuinely unequal — say the account is documented as 70% one partner's contribution and 30% the other's — the share entered should reflect that actual split, not an automatic half. This matters because understating the S1 holder's true share means paying more social charges than necessary, and overstating it risks a challenge if the tax office asks for evidence of the ownership split.
What counts as evidence of an unequal split:
- Account opening documents showing unequal initial contributions
- A marriage contract or matrimonial regime that keeps assets separate rather than pooled
- Property deeds showing an unequal ownership percentage
If your accounts and property are all held jointly with no documented unequal split, 50/50 is the reasonable and defensible default.
Which Income Types This Applies To — and the Exact Boxes
The reduced 7.5% solidarity levy — in place of the standard 17.2% or 18.6% — applies to the S1 holder's isolated share, entered in one of four dedicated boxes on Form 2042-C:
| Box | Income type |
|---|---|
| 8RF | Rental income (after the micro-régime allowance, if that regime applies) |
| 8RV | Purchased life annuities (rentes viagères à titre onéreux), net after allowance |
| 8RC | Dividends, interest, and Assurance Vie gains |
| 8RM | Capital gains on securities |
The form itself is explicit about when to use this block: it states plainly that these boxes are filled in only if you are married or PACS'd and only one of the two spouses meets the S1 condition — in other words, this section exists specifically for the mixed-household case this article covers.
Assurance Vie shares 8RC with dividends and interest, rather than getting its own box. This makes sense once you know how an Assurance Vie gain is actually declared elsewhere on the return: it's filed under "revenus de capitaux mobiliers" — income from movable capital, the same broad category dividends and interest belong to — not as a separate income type of its own. So an S1 holder's isolated share of an Assurance Vie gain goes into 8RC alongside any dividend or interest income, added together as one combined figure.
Pension income works differently again. For pension income specifically, the S1 exemption is generally assessed per-recipient rather than as a shared joint figure, since a pension is paid to one named person. If both of you receive separate pensions and only one of you holds an S1, that partner's own pension is the one that benefits — there's no splitting calculation needed because the income was never joint in the first place.
What Happens If You Don't Declare the Split
Missing this declaration doesn't reliably work in your favour. Depending on how the return is processed, you may end up with the full standard rate applied to the entire joint income — including the S1 holder's rightful share — because nothing on the return told the tax office to isolate it.
This is the same underlying problem covered in The S1 Holder Who Forgets to Tell Impôts: a real S1, correctly registered with CPAM, delivers nothing on your tax bill unless the declaration side is also done correctly — and in a mixed household, that declaration has an extra step.
Common Mistakes in Mixed S1 Households
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Assuming one partner's S1 halves the whole household's social charges automatically. It only reduces the S1 holder's specific, isolated share — and only if that share is actually declared separately.
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Defaulting to 50/50 when ownership is genuinely unequal. If you can document a different split, use it. Sticking to an inaccurate 50/50 by default either overpays or underpays social charges depending on which direction the real ownership split runs.
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Treating pension income the same as joint investment income. Pensions are generally assessed per-recipient, not split — if you're trying to apply a 50/50 calculation to a pension that's paid to one of you individually, that's the wrong mechanism entirely.
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Using the wrong box for the income type. 8RF, 8RV, 8RC, and 8RM each cover a specific category — rental income, purchased annuities, dividends/interest/Assurance Vie combined, and securities gains respectively. Entering a figure in the wrong box means it isn't correctly excluded from the joint social charges calculation.
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Not keeping evidence of an unequal ownership split. If you're claiming anything other than 50/50, keep the documentation that supports it — account statements, marriage contract, property deed — in case the tax office asks.
Frequently Asked Questions
My partner has an S1 and I don't. Does that reduce social charges on our whole joint account?
No — only on your partner's isolated share of that account, and only if that share is declared separately on the return. Without the split being declared, the reduction doesn't apply correctly to the joint total.
How do we work out each partner's share of a joint account?
Start from a 50/50 default for jointly held assets. If you can document a genuinely unequal ownership split — through account records, a marriage contract, or property deeds — use that actual split instead.
Does this apply to pension income too?
Generally not in the same way. Pension income is usually assessed per-recipient rather than as a joint figure to be split, since a pension is paid to one named person. If only one partner holds an S1, that partner's own pension is what benefits.
What box do I use to declare the split?
It depends on the income type: 8RF for rental income, 8RV for purchased life annuities, 8RC for dividends, interest, and Assurance Vie gains combined, and 8RM for capital gains on securities. These boxes are explicitly labelled on Form 2042-C for use only when one spouse holds an S1 and the other doesn't.
Does this apply to Assurance Vie gains too?
Yes. An Assurance Vie gain is declared under the same "revenus de capitaux mobiliers" category as dividends and interest, so an S1 holder's isolated share goes into 8RC alongside any dividend or interest income, combined into one figure rather than kept separate.
What happens if we just don't declare a split at all?
Depending on how the return is processed, the tax office may apply the full standard rate to the whole joint amount, including the S1 holder's rightful share. There's no guarantee the system defaults in your favour if the split isn't stated.
We're not married or PACS'd — does any of this still apply?
The core principle — that an S1 only reduces the S1 holder's own share of income, not a partner's — still applies to cohabiting couples. However, unmarried and non-PACS'd couples don't share a single foyer fiscal in the same way, so how jointly held assets and income are treated can differ. If this applies to you, it's worth confirming the household-filing implications separately.
Sources: Form 2042 — Déclaration des revenus (official form page; the Form 2042-C supplementary form, Cerfa n°11222, "Revenus du patrimoine exonérés de CSG et de CRDS" section, confirms boxes 8SH/8SI and the mixed-household-only 8RF/8RV/8RC/8RM block with its exact stated condition, "uniquement si vous êtes mariés ou pacsés et si un seul des deux conjoints remplit la condition ci-dessus") · this project's own IG-5 (Assurance Vie) guidance file (confirms box 8RC as the mixed-household entry point for an S1 holder's share of an Assurance Vie gain, consistent with Assurance Vie being declared under the same "revenus de capitaux mobiliers" category as dividends and interest elsewhere on the return) · s1-explained-uk-expats-france.md and no-s1-social-charges-declaration-france.md (this project's own verified figures for the S1 mechanism and social charges rates, reused here without re-deriving)