What should I do with the history from a closed exchange?

This help page provides guidance for those who have experienced transactions at closed exchanges and cannot obtain transaction histories.

Please note that if transaction histories cannot be obtained, the resulting profit and loss calculations will not be 100% accurate. Ultimately, the tax office will determine whether the following processing methods are acceptable.

STEP 1: Upload all transactions from exchanges other than the closed ones

If "invalid transactions" occur when all transactions from exchanges other than the closed ones are uploaded, it is assumed that this is due to the absence of history from the closed exchange.

How to upload trade history

STEP 2: Resolve all invalid transactions

For transactions with insufficient coins (if the transaction was a buy/sell), add purchase transactions for the missing amount. (In this case, the price should be roughly the market value.)

Once the oldest invalid transaction is resolved, subsequent invalid transactions may be resolved sequentially. Repeat the above corrections to resolve all invalid transactions first.

How to fix invalid transactions caused by "Insufficient position"

STEP 3: Compare with actual coin holdings and add probable transactions

With no invalid transactions, check for discrepancies with your actual coin holdings.
If the missing transactions were buy/sell and you have a rough idea of the period, add buy/sell transactions for that period proportionally to match your actual holdings.

If the calculation results show a deficit, add buy transactions, and if there is a surplus, add sell transactions in JPY for the surplus/deficit amount.

How to adjust the coin position after fixing all invalid transactions

【Example】The calculation results (after resolving all invalid transactions) show 3 more BTC than actual. It is believed that BTC transactions were conducted around January to June 2022.

Add transactions selling 0.5 BTC each at the end of each month in JPY.
(If described in a custom file, leaving the Price field blank will automatically refer to the market value.)
Even if the actual transactions were not in JPY, it is not a problem. For profit and loss calculations, it needs to be evaluated in JPY, so treat it as a JPY sale.
If this added sale transaction causes further invalid transactions, adjust by changing the proportional method, such as selling 3 BTC at the end of June or doing so on a later date.