The date of your arrival (which is the date mentioned on your work permit) is usually considered as the start date of your Swiss tax residency. Depending on the canton, the date might move to the beginning of a month. This means, your residency status in Switzerland might change during the year and you might be Swiss tax resident for part of the year only.
Should your family reach Switzerland at a different date, you might even be non-resident at first and then become tax resident. Please reach out to your Deloitte contact, should this be the case in your situation.
Please ensure you have your calendar on www.gadeloitte.com up to date for the entire calendar year, indicating your Swiss and foreign work and non-workdays. Also, inform your Deloitte Switzerland representative that you might become tax liable on Swiss workdays prior to your Swiss tax residency period. Your Deloitte contact will then identify the next steps with you.
In principle, there is an automatic exchange of information between the Swiss immigration authorities and the cantonal tax authorities. Consequently, you should automatically be registered to the Swiss tax authorities as soon as your work permit is issued.
However, depending on the canton/commune where you live, you may have to register to your commune of residence.