How long am I allowed to stay in Japan?

I'm currently attending japanese school but I am planning to end the course earlier and graduate in April.
Here is the matter:
The period of stay registered on my zairyu card (residence card) is until January 1st 2022.
As well as the visa on my passport, it says 許可期限 : 2022年1月1日.
Then my student card expires in September 30th.

How long am I actually allowed to stay in Japan if decide to graduate in April?
You might say "you shoul ask to your teachers" but I've asked them 3 times and I've been told different things everytime it's like they're kidding me.

Anyone knows? Thank you very much in advance

So your student card is until Sept. 2021, you will be graduating in April 2021, and the current resident status is until Jan. 2022?

As far as I understand the rules, if you graduate (= no longer a student), you’d need to report the fact to the immigration bureau within 14 days of that happening. And after that: (a) if you want to continue studying in Japan, enroll in another school/another course, which is also full-time, within a few months, and update the resident card with the new school as the sponsor (b) if you want to travel within Japan before returning home (COVID permitting), or want a few months to clear out of our apartment, etc., change your resident status to “temporary visitor” by visiting the immigration bureau, or (c) if you want to stay in Japan to look for a job in Japan, apply at the immigration bureau for a resident status to “designated activities” which allows you to stay in Japan after-studies for job-hunting purposes.

Seeing the several months’ difference between your student card expiry date and the resident status expiry date, isn’t it that you were originally planning to study till Sept., and you had a few months allowed already into the visa period to allow for time to get ready and move out of your apartment, etc.? Then (b) might not be possible.

If that is the case, I’d say 3 months beyond your studies, so probably until around June if you graduate in April. In any case, if you do graduate, inform immigration authorities of the change within 14 days.

Thank you for replying AK it`s more clear now.
Yes the original plan was to study until September but due to some economic problems related to covid I`m thinking to graduate earlier around April 2021.

So I could change my status to “temporary visitor” but I guess I wouldn`t be able to work part-time right.
I`ve also heard about the “designated activities” status, but I`m still doing my researches cause I don`t think everyone is eligible for 特定活動ビザ.
Typically japanese language students are not eligible for it, but someone says this year because of covid, also japanese language students can get it.

you can't work, after you leave the school, even if you don't change the status.
the 28 hr work permission is valid, only when you go to school.

90 days from end of studies.

Dont choose to graduate earlier if you wanna stay longer.

As an observation, changing to "temporary visitor" might be difficult given the current suspension of things like the visa waiver programme and the fact visas are not being issued for tourism purposes. The situation might be different because you are in the country.

「You might say "you shoul ask to your teachers" but I've asked them 3 times and I've been told different things everytime it's like they're kidding me.」

If I had to guess, I'd say your teachers aren't kidding you so much as they don't know. Unless you're studying immigration law, if you have a question about your visa status your teachers aren't the people you should be asking. Instead, ask your school's administrators, such as whoever is in charge of admissions or visa liaison work. If they can't give you the information you need, ask the immigration bureau. But if you're expecting your Japanese language classroom instructors to be experts in visa regulations, that's probably outside their area of expertise.

Thank you guys for your help.
I sent an email to the immigration bureau asking about 特定活動ビザ
if I could go with that it would be great.