INASTI Social Contributions for Self-Employed in Belgium: Calculation, Thresholds and Reductions

Key takeaways

• The social contribution rate is 20.50% on net income up to €75,024.54, and 14.16% on the next tranche up to €110,562.42.
• The minimum quarterly contribution is €890.42 in 2026, due even when income is low.
• Contributions are first provisional (calculated on N-3 income), then regularised once definitive income is known.
• Complementary self-employed persons whose annual net income stays below €1,922.16 pay no contributions.
• Primostarters benefit from a reduced minimum contribution during their first four quarters.

INASTI social contributions for self-employed workers in Belgium are often one of the first financial surprises for new independents. Unlike salaried employees, no employer automatically deducts these charges: the self-employed person calculates them, anticipates them and pays them quarterly to their social insurance fund. In 2026, the main rate is 20.50% on net professional income, with a minimum quarterly contribution of €890.42. This guide covers the exact calculation, the thresholds in force, specific cases and the steps needed to stay compliant from day one.

Who is subject to INASTI social contributions

Every Belgian self-employed worker, whether operating as a principal or complementary activity, is subject to the social insurance scheme for self-employed workers managed by INASTI (National Institute for the Social Insurance of the Self-Employed). This status covers sole traders, managers of private limited companies (SRL/BV), directors of public limited companies (SA/NV) and active partners in a company.

Affiliation must be arranged with an approved social insurance fund (Acerta, Partena Professional, Liantis, Securex, Xerius, UCM, etc.) or with the National Auxiliary Fund. This affiliation must be in place before the activity begins and is separate from registration at the Crossroads Bank for Enterprises (CBE/KBO).

Calculating INASTI contributions: rates and tranches

Social contributions are calculated on the net taxable professional income for the current year. This income corresponds to professional profit after deduction of professional expenses, as it will appear in the tax return.

The minimum reference income for calculating the minimum contribution is set at €17,374.08 in 2026. A self-employed person whose income falls below this threshold still pays the minimum contribution, unless they fall under a specific scheme (starters, low-income complementary workers).

The maximum quarterly contribution is €5,103.05, corresponding to both tranches applied up to the ceiling of €110,562.42. Beyond that ceiling, additional income generates no further social contributions.

Provisional contributions and final regularisation

The INASTI contribution payment mechanism works in two stages, which often surprises new self-employed persons.

During year N, contributions are provisional: they are calculated on the basis of income from year N-3 (three years earlier), communicated by the tax authority to the social insurance fund. If you are starting your activity and have no reference income yet, provisional flat-rate contributions apply.

Once the tax authority has processed your return for year N and communicated your actual income to your fund, a regularisation takes place:

• If your provisional contributions were insufficient compared to your actual income, you receive a regularisation notice.
• If they were too high, a refund is calculated.

The quarterly payment schedule

Contributions are due four times a year, before the following deadlines:

1. 1

   1st quarter

   31 March

   Payment due by 31 March of the current year. This instalment covers the provisional contributions for the current quarter.

2. 2

   2nd quarter

   30 June

   Payment due by 30 June. If a regularisation surcharge arose from the previous year, it may appear at this point.

3. 3

   3rd quarter

   30 September

   Payment due by 30 September. Provisional contributions remain based on N-3 income until regularisation.

4. 4

   4th quarter

   31 December

   Payment due by 31 December. This is the last deadline of the calendar year.

Any insufficient or late payment attracts surcharges. INASTI also provides the option to request an exemption from contributions in cases of genuine financial difficulty, subject to conditions.

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Special cases: complementary, starters and assisting spouses

The standard rules apply to principal self-employed persons. Several categories benefit from adapted rules.

	Exemption threshold	Applicable rate	Minimum contribution
Principal activity	None	20.50% then 14.16%	Yes (€890.42/quarter)
Complementary (low income)	< €1,922.16/year	Reduced from €1,922.16 to €17,374.08	No
Primostarter	None	20.50% then 14.16%	Yes, reduced (first 4 quarters)
Assisting spouse (maxi-status)	None	Same basis as principal	Yes

For a complementary self-employed person whose annual net income exceeds €17,374.08, the standard rates (20.50% then 14.16%) apply in full, with no benefit linked to complementary status.

Primostarters, meaning persons creating their first principal self-employed activity, benefit from a reduced minimum contribution during their first four quarters of activity. This reduction is granted automatically by the fund at definitive calculation. From the fifth quarter onwards, standard rules apply. INASTI provides an extended period of eight quarters for self-employed artists (since 1 October 2022).

What social contributions cover

INASTI contributions are not a tax in the strict sense. They open real social rights for the self-employed person and, depending on the scheme, for their family:

Rights opened by INASTI contributions

• Retirement pension

  Accumulation of pension entitlements under the self-employed scheme, calculated on career length and income.

• Health and disability insurance

  Coverage of healthcare costs and income replacement in the event of long-term incapacity to work.

• Family allowances

  Entitlement to family allowances for dependent children, managed by family allowance funds.

• Maternity and paternity insurance

  Flat-rate allowance at birth and recognised partial interruption of activity.

• Bridging right

  Income-replacement allowance in the event of bankruptcy, forced cessation or certain life events (serious illness, domestic violence).

The quality of these rights depends on valid contribution quarters: a quarter is recognised if the minimum quarterly amount is reached. A quarter with an insufficient minimum contribution can reduce the rights accrued for the period concerned.

Further reading

• VAT for self-employed in Belgium: thresholds and obligations to understand the two main tax obligations that apply from the start of an activity.
• Complementary self-employed in Belgium to understand the status and specific thresholds that apply alongside a salaried position.
• Tax reform 2026: what changes for self-employed persons to follow recent developments affecting the social status of Belgian self-employed workers.