I
think your understanding is correct. But I am just another person on a website, so you shouldn't base your decisions just on me. To be absolutely certain that what you do is going to give the outcome you want, contact both the Inland Revenue and INZ.
but i am considered now as Tax resident as i am having residence since January 2012 , so i am from that time tax resident , or from the time i start my job with the silver fern work visa which is August 2011 ??
Notice that on the Inland Revenue website, they specifically mention that their definition of resident can be different from what is used by immigration.
For the Inland Revenue, I think you are
tax resident since you started working in August 2011, but that doesn't count
for INZ when they're looking at eligibility for PR. INZ say this.
You have been in New Zealand as a resident for a total of 41 days or more in each of the two 12-month portions of the 24 months immediately preceding your permanent resident visa application, and you are assessed by Inland Revenue (IR) as holding tax residence status for the two years preceding your application for a permanent resident visa.
As you see, they're not counting two years of tax residence FROM WHEN YOU FIRST BECAME TAX RESIDENT. They're counting two years BACK from when you apply for PR, and that can only be on a date two years AFTER you obtain your Residence visa.