How to prove crypto cost basis when exchange records are gone

27 September 2026

If your crypto exchange records are gone, you can still reconstruct and prove your cost basis - the original value you paid for an asset - using any combination of your own transaction history, blockchain data, and third-party records. The IRS does not require a single document; it requires a reasonable, good-faith reconstruction that you can explain and support. The process is tedious, but it is not impossible, and doing it before you file is far cheaper than doing it after an audit letter arrives.

Why the cost basis matters

Your cost basis is the number that determines your taxable gain or loss when you sell, trade, or spend crypto. If you cannot prove it, the IRS may treat the entire sale proceeds as taxable gain - meaning you pay tax on money you never actually made. The burden of proof is on you, not the IRS. That is why reconstructing records is not optional if you have traded across multiple years and no longer have exchange statements.

Step 1: inventory what you still have

Before you start digging through old drives and email threads, take stock of what remains. You might have more than you think.

• Email receipts: Most exchanges send trade confirmations. Search your inbox for the exchange name, "trade executed," "withdrawal confirmed," or "purchase."
• Bank and card statements: Deposits and withdrawals show fiat amounts, but not which crypto you bought. Still, they establish a timeline and total fiat invested.
• Wallet files and seed phrases: If you hold keys, your addresses are on the blockchain. You can see every incoming transaction, but you cannot see the dollar value at the time without also knowing the date.
• Old tax software files: If you used TurboTax, CoinTracker, or Koinly in past years, export the prior-year tax reports. Those contain your own cost basis data, even if the exchange is now defunct.
• Hardware wallets: The device itself may have transaction history for the addresses it controls.

Write down every exchange, wallet, and address you can recall. Do not skip the ones with tiny balances - small accounts often cause the biggest headaches later.

Step 2: Pull Blockchain History for On-Chain Addresses

For any address you control, you can use a blockchain explorer (like Etherscan for Ethereum, or a block explorer for Bitcoin) to list every transaction. Export that data as a CSV file. That gives you dates, amounts, and the sending or receiving address - but not dollar values.

What this does give you is a complete list of every acquisition and disposition. You now know exactly what you held and when you moved it. What you still need is the dollar value on the date of each purchase.

Step 3: Reconstruct Prices on the Dates You Transacted

Once you have dates and amounts, you need historical price data. You do not need a paid service for this. Public sources include:

• CoinMarketCap and CoinGecko - both offer historical price charts and downloadable daily data for most coins.
• Exchange historical data pages - some exchanges publish daily OHLCV (open, high, low, close) data.
• Wayback Machine - if you know you bought on a specific date, you can often find a snapshot of the exchange’s price page for that day.

For each transaction, record the date, the amount, and the price on that date. Multiply to get the cost basis. Do this for every purchase, airdrop, staking reward, or other acquisition. Do not forget that fees count as part of the cost basis - if you paid a trading fee in crypto or fiat, that fee increases your basis.

Step 4: Build a Simple Ledger

A spreadsheet is fine. Columns should include at minimum: date, transaction type (buy, sell, trade, fee, reward), asset, amount, price per unit, and total value in USD. Then calculate your gain or loss per sale using whatever cost basis method you have already chosen (FIFO, LIFO, HIFO, or specific ID - covered elsewhere on this site).

Keep it simple. You do not need fancy software. You need a clear, chronological record that an auditor can follow.

Step 5: Write a Statement of Reconstruction

The IRS accepts what is often called a "statement of facts" - a written explanation of how you rebuilt your records. This is not a legal filing, but it serves as evidence of good faith. In it, state:

• That exchange records were lost due to closure, account deletion, or technical failure.
• What sources you used to reconstruct the data (blockchain explorers, email receipts, bank statements).
• The method you used to assign prices to historical dates.
• That you are reporting to the best of your ability based on available information.

Sign and date it. Attach it to your tax return, or keep it with your other records in case of an audit. This statement will not automatically excuse mistakes, but it demonstrates that you did not simply guess or ignore the issue.

Common mistakes to avoid

• Using the current price instead of the historical price. This seems obvious, but it is the most common error. Your cost basis is what you paid then, not what the coin is worth now.
• Forgetting about hard forks and airdrops. If you received new coins from a fork, your cost basis in those coins is typically zero (or the fair market value at receipt, depending on the circumstances). You still have to track them.
• Assuming a dead exchange means no records exist. The exchange may have been acquired, and the new owner may have exported customer data. Search for the exchange name plus "acquisition" or "customer data."
• Ignoring partial-year gaps. If you cannot reconstruct even one trade, the entire year's return may be flagged. Rebuild everything you can, and document what you cannot.

What if you truly cannot reconstruct anything?

If you have no records at all - no email, no bank statements, no wallet export - you are not without options. You can estimate your cost basis using the best available data, but you must be conservative. The IRS has no sympathy for "I lost it all" without a paper trail. Report the full proceeds as a gain if you have no basis evidence. You will overpay tax, but you will avoid a fraud penalty. If you later find records, you can amend the return.

The Bottom Line

Reconstructing cost basis is a research problem, not a legal battle. You do not need perfect data; you need a good-faith effort that you can explain. Start with what you have, use public blockchain data to fill gaps, and write down everything. A few hours of spreadsheet work now can save you thousands in tax, and it will make an audit far less painful if one ever comes.

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