A lot of people assume that the termination notice is always 3 months and that this is “by Norwegian law”.
The contract indeed can state explicitly 3 months as the termination notice. The countdown for these months starts with the month AFTER the resignation took place. So if you resign any day in September, the three months will be counted from the 1st October and your official employment will terminate on 31st of December.
However, the contract might not mention 3 months but instead say that "the termination notice is in accordance with the applicable law" and it can refer to "Working Environment Act" or "Arbeidsmiljøloven" in Norwegian (specifically "AML 15-3"). If you see this sentence, please note that it does not necessarily mean 3 months-notice.
A lot of people would be surprised to see that not everyone will get 3 months termination notice “by law”. You will see that, according to law, the termination notice will actually depend on your age and how long you have been working in this particular company.
*the termination notice can never be longer than 3 months if you resign yourself.
As you can see, the termination notice is 3 months only if you have been working for the same company longer than 10 years.
If you have any questions, please ask me here.