If the new exchange's tax form shows a cost basis of $0, does that mean I'm guaranteed to be overtaxed?
Not necessarily taxed on money you don't actually owe — but you will be systematically overestimated on taxable income unless you can supply the correct cost basis yourself and file accordingly. A Form 1099-DA or similar report generated by an exchange is one reference document submitted to tax authorities, not the sole basis for your filing — if you have the original transaction records, you can still use the correct cost basis when filing, rather than accepting the $0 shown on the exchange's report at face value. The catch is you need to have actually preserved that original record and be able to produce it if audited.
This is also why the real risk of "cost basis stranded on the old platform" isn't that tax law becomes stricter — it's that you lose the evidence needed to assert the correct number.
If my crypto tax software already auto-syncs multiple exchanges via API, do I still need to manually export a CSV?
API syncing does cut down significantly on manual work, but what it solves is "whether the software can keep seeing your activity across platforms" — that's not quite the same as "whether that connection still works after the old account is closed." Many exchanges deactivate API keys once an account is closed or downgraded to guest-only access, so if you close the old account first and only think about exporting data afterward, the API link may already be dead. The safer approach is to manually export a full CSV backup at the moment you decide to switch exchanges, even if API syncing is already running — treat the two as backing each other up, not as substitutes for one another.
If the old exchange collapses or gets forcibly shut down by regulators before I have a chance to export anything, is there still a way to recover?
This is the toughest scenario, but it doesn't mean there's no path forward. Start by checking whether you ever downloaded any form of record yourself — monthly statements, quarterly tax reports, or even transaction details buried in phone notifications or email confirmations. Piecing together these scattered fragments can often still reconstruct the approximate timing and price of most transactions. If the exchange's collapse involves bankruptcy proceedings, the bankruptcy trustee or successor entity sometimes opens a process for creditors to request their historical account data — it's worth watching for related announcements.
For whatever genuinely can't be reconstructed, the conservative filing principle is: rather than inventing a cost basis that happens to favor you, honestly record that the cost basis for that batch is unknown, and use the most conservative estimation approach available (the one least favorable to you and lowest-risk for your filing), while keeping a record of the process you went through trying to reconstruct the data, in case you're asked about it later.
Besides cost basis, what other easily-overlooked but tax-relevant details come up when switching exchanges?
One of the most commonly missed details is wallet address and account linkage tracking — if your crypto tax software relies on this linkage to determine which transactions are "internal transfers between your own accounts" (non-taxable) versus "sales to a third party" (taxable), failing to correctly flag the relationship between your old and new accounts during a switch can cause the software to misclassify an internal transfer as a sale, resulting in taxable income being double-counted. In practice, it's worth manually confirming in the software immediately after a transfer completes that the incoming transaction is classified as an "internal transfer" rather than a "new purchase," so this easily-overlooked classification error doesn't stack on top of the cost-basis problem.
Whether it's due to fees, regulatory pressure (some exchanges have exited certain jurisdictions), or simply wanting a smoother interface, sooner or later you'll need to move assets and transaction history from one exchange to another. Most people only care about whether the funds actually arrived — and overlook the thing most likely to break during the move: cost basis continuity. Moving the asset itself is simple, a single on-chain or internal transfer does it, but the information of "how much this asset originally cost" is typically something the new exchange has no visibility into, unless you actively bring it along.
When you transfer BTC from Exchange A to Exchange B, Exchange B's system only sees "a BTC deposit arrived at a certain time" — it has no automatic way of knowing whether that BTC was bought three years ago for $20,000 or last month for $60,000. If you later sell that BTC on Exchange B, the tax form it generates (such as a Form 1099-DA) may well show a cost basis of $0, or leave it blank entirely, because it has no record of your original purchase on Exchange A. If you haven't kept your own records by that point, you effectively end up overpaying tax on gains you never actually made.
First, export your complete transaction history before closing or scaling back the old account — most exchanges allow you to export a full CSV of your trading history, including timestamps and prices for every buy, sell, deposit, and withdrawal. This raw data is the foundation everything else is calculated from, and it's difficult to recover once lost. Second, make sure the export covers every one of your holding lots — if you use specific identification or HIFO for cost basis, you need the original price of each individual purchase lot preserved intact, not just a single averaged-out figure. Third, import the exported records into your crypto tax software so the software has already recorded the correct cost basis for these assets before the actual transfer happens — that way it can correctly match them once you sell on the new exchange. Fourth, screenshot or archive the blockchain transaction hash (tx hash) before and after the transfer as proof that the asset genuinely moved from the old platform to the new one, rather than being an independent new purchase — this becomes especially important if an audit later asks about the asset's origin. Fifth, avoid trading at the same time as the transfer — for example, placing buy or sell orders on the new platform while the transfer is still in progress — since this can cause cost-basis tracking software to conflate "the asset that was transferred in" with "an asset newly purchased." It's best to wait until the transfer is fully confirmed and the software has correctly identified the cost basis of those assets before taking your next action.
If the assets have already moved to the new platform and the old exchange account is deactivated or hard to log into again, there's still room to fix things. Most exchanges retain historical records for some period even after an account is closed, so contact support first to request a full transaction history. If the old exchange has shut down entirely (for example, forced out of the market by regulatory issues), the fallback is to gather whatever screenshots, statements, or wallet transfer records you still have on hand and reconstruct the original purchase price as best you can — then report conservatively and note your estimation method when filing. That's still far better than having no record at all and letting the system default your cost basis to zero.
When cost basis gets stranded on an old platform, the most direct consequence is that the new platform's tax form underestimates your cost basis (or shows it as zero), causing your sale to be calculated as generating far more taxable income than you actually made — meaning you overpay tax you never should have owed. This problem usually doesn't surface at the moment of transfer; it tends to show up only once you actually sell the asset and notice the numbers on the report look wrong, at which point reconstructing the old exchange's historical records is far harder than exporting them at the time of the switch would have been. Switching exchanges itself isn't a taxable event, but it's an easily overlooked recordkeeping checkpoint — one worth spending ten minutes on before you hit the transfer button.