Additional employer's tax shall be calculated from the calendar month the limit of NOK 750,000 is exceeded, and for the part that exceeds the amount limit. The basis for calculation is the basis for employer's contribution cf. National Insurance Act §23-3 with regulations.
Additional employer's tax shall not be calculated for the employer's contribution and premium payment to the collective pension scheme cf. Regulations on Additional Employer Tax §2
When the employee has worked for several registered subunits, additional employer's contributions may be reported in aggregate to the business in which the main unit is registered.
For employees who have multiple employers, the employment conditions will have to be looked at separately. If one deliberately divides a position in order to avoid additional employer tax, for example in a group of companies, this may result in a cut-off from the Tax Administration.
The additional employer's tax was originally supposed to apply to Svalbard as well, but on 16 January 2023 the Finansdepatemetet has adopted an amendment which means that the provision does not apply to Svalbard anyway. Read more here.
For more information see:
Regulations on Additional Employer Tax
Prop. 1 LS (2022-2023) point 5.1