Every year, self-employed workers must report their business income for two separate purposes: calculating income tax and calculating social security contributions. Since 2021, these two parts have been combined into a single online return on impots.gouv.fr. The principle seems straightforward, but the sections to complete vary depending on the tax regime, legal status and type of income received.
Gross social income: the new contribution base that changes how contributions are calculated
The reform of the social contribution base, which took effect for the 2025 income tax return, changes how Urssaf determines the basis for your social security contributions and levies. Previously, business income was used as the starting point after deducting mandatory social security contributions and deductible CSG. This circular mechanism is now gone.
A flat-rate allowance now replaces these deductions. For self-employed workers under the actual-profit regime, the business tax return includes a specific section for gross social income, which Urssaf uses directly. Those under the micro regime retain their own tax allowance, applied to turnover.
In practice, this means that contributory contributions (basic and supplementary pensions) increase proportionally, while the CSG-CRDS share decreases. The overall amount of social security levies remains the same as before the reform, but the allocation changes in favor of higher individual entitlements, particularly for retirement.
The guide covering what to declare to Urssaf and the tax authorities outlines all the sections affected by this reform for each regime.
Micro or actual-profit regime: different tax and social security sections
The exact contents of the return depend on the tax regime. Confusing the two processes can lead to errors in the amounts reported, affecting both tax and social security contributions.
Micro-BIC and micro-BNC
Under the micro regime, the return reports gross turnover or gross receipts. You should not apply the flat-rate allowance for expenses and charges yourself: the tax authorities and Urssaf each apply it separately to determine taxable net income and the social security contribution base.
- For micro-BIC sales, turnover is reported in section 5KO or 5LO, without deducting the expense allowance.
- For micro-BNC, gross receipts are reported in section 5HQ or 5IQ, again without applying the allowance.
- Daily maternity, paternity or adoption benefits paid by CPAM must not be included in these sections, as they are not taxable for this purpose.
Actual-profit BIC and BNC (controlled declaration)
Things work differently under the actual-profit regime. Income reported in the tax section of the return is no longer used directly by Urssaf to calculate contributions. Instead, the social security section is based on the gross social income shown in the business tax return.
An administrative concession allowed accountants to continue using the previous year’s tax return template while waiting for the forms to be updated. Before submitting the return, it is still worth checking that gross social income appears in the business tax return.
Platform income and side activities: what is actually taxable
Receiving an annual summary from an online platform does not mean that all the amounts shown are taxable. The tax authorities distinguish between different types of activity.
- Occasional sales of personal belongings (clothes, furniture, household appliances) are generally not taxable, unless they exceed certain thresholds or form part of a regular business activity.
- Buying or making goods for resale is a taxable commercial activity from the very first euro.
- Sharing costs for a carpool on a personal journey may be tax-exempt, provided the driver does not make a profit beyond sharing the actual costs.
Platforms now report income data to the tax authorities. An amount reported by a platform is not automatically taxable: taxpayers must check the nature of each payment before deciding whether to include it in their return.
Social security section of the combined return: don’t forget additional income
The social security section of the return is not limited to primary business income. Certain additional income must also be reported to ensure contributions are calculated correctly.
Replacement income reported in sections DSCZ or DSDZ includes, in particular, the daily caregiver allowance (AJPA) paid by CAF, as well as daily benefits received under a Madelin contract, excluding those related to a long-term illness.
Amounts received through profit-sharing, employee savings plans or employer contributions to a retirement savings plan, when exempt from income tax, must be reported in specific sections (DSPA/DSPB or DSQA/DSQB, depending on status). Omitting these amounts can distort the calculation of contributions without necessarily affecting tax, potentially leading to a later adjustment.
Self-employed micro-entrepreneurs are not covered by the unified social security and tax return. They continue to report their turnover directly to Urssaf monthly or quarterly, in addition to filing their regular income tax return.
The unified return must be filed online. Urssaf and the General Social Security Funds (CGSS for the DROM) remain the points of contact for managing and paying contributions, even though the return is completed through the tax portal. Checking each section against the relevant annual guidance is still the most reliable way to avoid discrepancies between the amount reported and the amount actually due.
