Exporting your transaction data

Fix the period first. Japanese income is computed on the calendar year, so aligning everything to 1 January through 31 December makes later work far easier. Across several years, keep a separate file per year. Exporting without deciding the period produces duplicates and omissions at the same time.

Then export from each service. Exchanges usually split trade history, deposit and withdrawal history, and fee records into separate files, and you need all of them. Some stop offering history beyond a certain age. If you plan to close an account, or a service announces it is shutting down, export before anything else.

On-chain activity can often be exported from an address page in an explorer. Native transfers, token transfers and internal transfers are usually separate exports, so taking only one leaves holes. Complex DeFi interactions are harder still, because a single transaction can move several assets and the export alone may not let you reconstruct what happened.

Then normalise the format. The fields to align are timestamp, transaction type, quantity, currency, counterparty, fee and the price used as your cost basis. Time deserves particular care: some services export in UTC and others in local time, and without a common basis year-end transactions land in the wrong year. When opening files in a spreadsheet, import long numbers and dates as text — automatic conversion quietly corrupts them.

Finally, gaps and storage. You will find them: fees not recorded separately, transfers where you cannot tell whether the destination was your own wallet or someone else's. Annotate what you can work out and keep the supporting screens and transaction hashes alongside. Remember that these files describe your entire position — decide where they live rather than leaving them in shared storage.