Occupational accident contribution (AT/MP): from gross to net rate

Sources and assumptions

• ameli.fr — tax year 2026, verified on September 17, 2026

  Excerpt from the source : « M1 : couvre le coût des accidents de trajet (en 2026 : M1 = 0,19 %) ; »

• ameli.fr — tax year 2026, verified on September 17, 2026

  Excerpt from the source : « M2 : couvre l'ensemble des frais de gestion du risque professionnel (en 2026 : M2 = 52 %) ; »

• ameli.fr — tax year 2026, verified on September 17, 2026

  Excerpt from the source : « M3 : couvre le coût des transferts vers les autres régimes et le fonds dédié à la prise en charge spécifique des salariés exposés à l'amiante (en 2026 : M3 = 0,17 %) ; »

• ameli.fr — tax year 2026, verified on September 17, 2026

  Excerpt from the source : « M4 : couvre le coût des dépenses liées à la prise en compte de la pénibilité (en 2026 : M4 = 0,03 %) ; »

• ameli.fr — tax year 2026, verified on September 17, 2026

  Excerpt from the source : « le taux collectif s’applique aux entreprises de moins de 20 salariés ; »

• ameli.fr — tax year 2026, verified on September 17, 2026

  Excerpt from the source : « le taux individuel s’applique aux entreprises de 150 salariés ou plus. »

• ameli.fr — tax year 2026, verified on September 17, 2026

  Excerpt from the source : « Il concerne les entreprises en tarification collective et mixte, c’est-à-dire avec moins de 150 salariés. »

• ameli.fr — tax year 2026, verified on September 17, 2026

  Excerpt from the source : « Les établissements créés depuis moins de trois ans et ceux relevant de certaines activités bénéficient du taux collectif, quel que soit leur nombre de salariés. »

Calculation assumptions

• The gross rate is an INPUT, not a value computed here: the schedule of collective rates is an annual ministerial order covering several hundred risk codes, and the mixed and individual rates depend on the establishment's own three-year claims record. Copy the gross rate from the calculation details of your rate, as set by the regional fund — an invented rate yields an invented contribution.
• The weighting between the collective and the individual rate that makes up the mixed rate from 20 to 149 employees is not modelled: the ameli.fr page states that the individual share grows with headcount, without publishing the formula. The engine starts from the already-composed gross rate, the one carried by the notification.
• The net rate is returned to four decimal places, the precision carried by a notified gross rate (two decimals) and by the (1 + M2) factor. The rounding applied by the fund to the notified rate is not modelled; a gap of one hundredth of a point may therefore remain against the actual contribution call.
• The base used is the gross annual payroll you enter. The engine does not rebuild the social-security contribution base (benefits in kind, allowances, ceilings), computes no other employer contribution and applies no relief — the general reduction in employer contributions is handled by its own engine, with its own rules.
• The headcount band entered prevails; it is set by the headcount of the last year known when the rate is calculated (for 2026 pricing, that of 2024), according to service-public.fr. The social-security headcount counting rules and the neutralisation that follows a threshold crossing are not modelled. Eligibility for the "administrative support functions" rate is judged on headcount below 150 alone, as the ameli.fr page itself glosses "collective and mixed pricing". Headcount thresholds differ in Alsace-Moselle (collective rate below 50 employees, mixed from 50 to 149, and up to 299 in construction): they are not modelled, and the pricing regime stated does not hold for those companies — the amount itself follows the same formula.