You may become a Norwegian tax resident after spending 271 days in Norway during any rolling 36-month period. Exactly 270 days does not trigger this test. This is an alternative to the one-year 184-day test, not an additional requirement, and the days must be counted across the full rolling period rather than as an annual 90-day allowance. For qualifying stays spread across multiple calendar years, residency generally starts on 1 January of the year in which the threshold is reached. This rule only tracks the initial day-count test and does not calculate the effective start date of tax residency. Once tax residency is established, it does not automatically end when days leave the rolling window; separate departure requirements apply.
https://www.skatteetaten.no/en/person/taxes/get-the-taxes-right/abroad/tax-when-you-move-to-norway/