When an exchange deposit is not a new lot

Transfers labeled as deposits silently reset cost basis. How to spot the pattern before you trust a realized P&L export.

Most exchange CSVs treat every inbound movement as an acquisition. That is convenient for the exchange. It is dangerous for tax-lot performance analysis.

If you withdrew BTC to a cold wallet and later deposited it back, the second deposit often appears as a brand-new buy at the deposit-time mark price — or with a zero cost if the export is incomplete. Your earlier acquisition lot vanishes from the exchange’s story even though economically nothing was sold.

What to inspect

Match withdrawal timestamps on venue A to deposit timestamps on venue B within a realistic travel window.
Compare quantities after network fees; small shortfalls are normal, large gaps need a note.
Keep a wallet map so “new” deposits that originate from your own addresses are flagged before matching sales.

Why high-volume books suffer more

Traders who move collateral weekly accumulate dozens of these false acquisitions. Average-cost tools paper over the problem until a large disposition hits the wrong basis. A short transfer reconciliation before a full lot review usually pays for itself in avoided adviser back-and-forth.

App Analytics flags these chains during intake. Bring deposit/withdrawal logs together with trade history; do not rely on the trades file alone.