Tax filing in Japan is complex and challenging.

However, if you are employed and have a side job, you are required to file individual tax returns.

You can find English-speaking tax accountants from the link below:

HP : https://www.fsa.go.jp/internationalfinancialcenter/multilingual-organizations 
(It is written in Japanese, I wonder how it reaches English speakers…)

Is it necessary to submit a business registration to the tax office?

In the case of a side job, if your income is relatively low compared to your salary, you should file your tax returns as “Miscellaneous income.”

In that case, you generally do not need to submit a business registration to the tax office.

If your side job grows in scale, you can file your them as “Business income.”

For “Business income, you need to submit a “business registration” to the tax office.

Additionally, by submitting an “Application for approval of blue return,” you can enjoy various tax benefits.

The National Tax Agency has also published methods for filing tax returns by youfself.

HP : https://www.nta.go.jp/taxes/shiraberu/shinkoku/tebiki/2023/pdf/061.pdf

Please refer to this flowchart for determining “Miscellaneous income” and “Business income.”
Reference : https://www.town.otaki.chiba.jp/kurashi/zei/7/1095.html

What documents are required?

The main documents required for your tax return filings are as follows.

• My Number information
• Tax withholding statement from a company you work for
  (For full-time workers, it’s called gensenchoshuhyou 源泉徴収票 in Japanese.)
  (For freelancers, it’s called shiharai chōsho 支払調書 in Japanses.)
• Documents related to revenue for your side job
• Invoices and receipts for all deductibles
  This is broad and can include all expenses related to your work.
  For example, if you work from home, you can deduct some portion of your rent and utility bills.
• Your banking information and/or bank statement

When should you file your tax returns?

Your tax liabilities are calculated based on the calendar year (i.e. From 1st January to 31st December).

The filing period is from February 16 to March 15 of the following year.

The individual tax payment must be made by March 15.

If you set up automatic bank transfers, the tax will be withdrawn from your bank account in late April.

Additionally, the resident tax payment notice will arrive around May.

Payment can be made at bank counters, convenience stores, or through online banking.

It is important to note that the individual tax and the resident tax are paid separately.

While you can handle your tax returns for your side job on your own, it can be time-consuming and labor-intensive. Therefore, consider consulting with a Japanese tax accountant who can communicate in English.