Tax Purposes - Permanent Resident

For tax purposes, when does permanent resident status kick in?

This site (and elsewhere) say 5 year. Now is that five full years (1826 days, give or take a leap day) or is it five calendar years? And if it is calendar years, does the first year I live in Japan count as Year-Zero or Year-One?

Say I arrived in Japan on April 1, 2011. When exactly would I be considered a permanent resident (as far as the taxman is concerned)? Would it be:

January 1, 2015?
January 1, 2016?
April 1, 2016?
Or some other date?

No matter how much I search, I cannot seem to find the answer. Logically I know which date seems like the correct answer, but I know logic and government regulations don't always mix.

I would greatly appreciate some help. And if you could link me to an official government document that references this, that would be awesome.

Thank you so much in advance.

Pardon me for bumping my own thread. If I don't get a answer, I will just let this thread quietly go away.

what is your current income ? Does a company pay your salary ?
what is your current health insurance ?

About 220,000 a month. Salary from employer. National taxes withheld. Local taxes self-paid. National Health Insurance.

I am looking at the explanation on resident status as described in the "Confirmation of the Type of Resident Status, Etc." form, which non-Japanese residents filing taxes need to submit. (My husband is non-Japanese, and is not a salaried worker, so he needs to submit this form. That is why I get to see this document.)

Begin quote:
The following is a brief explanation of resident status.

(1) Resident
A person who has a "JUSHO" (domicile) in Japan, or has had a "KYOSHO" (residence) in Japan for one year or more.

(i) Non-permanent resident
A resident who has not Japanese nationality and has had his/her "JUSHO" or "KYOSHO" in Japan for period or periods in the aggregate 5 years or less in last 10 years.
(ii) Permanent resident
A resident other than non-permanent resident.

End quote.

THere is also a table where they say you can list your dates of arrival in Japan and departure from Japan as stamped in your passport (for the past ten years) and use it as evidence of your resident status. So they really mean adding up all the dates to see if your stays reach "aggregate 5 years" or not.

So non-permanent is "the aggregate 5 years or less". Which means permeant is 5 years (365x5) + one day, it seems.

Thank you for that. Huge help!

And thank you for mentioning that specific document. I will give it a look over later tonight (if I can find it online). Do you happen to know the Japanese name of that document?

Again, thank you so much.

居住形態等に関する確認書 it is in Japanese.