It's based on guidance released by the NTA on the 1st of December regarding crypto tax (https://www.nta.go.jp/shiraberu/zeiho-k ... 127/01.pdf).
This is the most comprehensive info I have found to date, covering even forks and mining. Although not extremely detailed, it pretty much answered all my questions in regards to what is taxable and how to calculate it.
It's pretty much what I was expecting. That is, use a moving average/adjusted cost base to calculate your running acquisition cost when making multiple transactions of the same currency. And when buying one currency with another currency, that is also a tax event.
Profits made should be declared in your tax return as "zatsushotoku" (miscellaneous income). If you normally don't need to submit a kakutei shinkoku, and your profits are less than 200,000 yen, there is no need to report these profits. However, I read on another site that you will still be liable to pay citizen's tax on those profits (https://btcnews.jp/3b2pzy9m12639).
The article also spells out that not paying tax properly for crypto amounts to tax evasion, and details the potential punishments.
This image is also interesting. It shows the tax rates for different bitcoin profits. This would suggest that it's taxed separately to your overall income (I thought it was included?). Maybe this is how miscellaneous income works? I'm not sure... Anyway, say you make less than 3,300,000 yen profit in a year. There's a deductible amount of around 100,000 yen. And the tax rate on the remainder is 10%, plus 10% citizen tax = total 20% tax.
If you have any questions in regards to translation of the doc, just ask me.
