What Happens if You Lost the CSV from a Closed Exchange?

02 November 2026

You lose the ability to automatically reconstruct your trade history and cost basis for that exchange's activity. Without the CSV, you must manually piece together your records from whatever sources remain, and the difficulty of that task depends on how much other data you saved outside the exchange.

Why the CSV mattered

When an exchange shuts down, its API stops working and its web interface disappears. The CSV export you downloaded before closure was your only structured record of every trade, deposit, withdrawal, and fee. It contained timestamps, amounts, trading pairs, and transaction IDs - information that portfolio tracking software reads directly to calculate gains and losses.

Without that file, you have no single authoritative source for what happened inside that exchange. Your portfolio tracker will show a gap in your history, and any tax report you generate will miss those trades unless you fill in the missing data manually.

What you still might have

Even without the CSV, you may hold several pieces of the puzzle:

• Email confirmations from the exchange for each trade, deposit, or withdrawal. Most exchanges send a confirmation email for every transaction. Search your inbox for the exchange's domain and collect every message.
• Bank or card statements showing fiat deposits or withdrawals to and from the exchange. These prove you moved money in or out, but they don't show what you traded or at what price.
• Blockchain transaction records for any crypto you sent to or from the exchange. A wallet's transaction history shows the amount and the destination or source address, but not the exchange's internal trade details.
• Screenshots or manual notes you may have taken of your balance, open orders, or trade history while the exchange was still live.
• Tax reports or portfolio snapshots you generated while the exchange was operational. These may contain summary data even if the raw trade list is gone.

How to Reconstruct the Missing History

Step 1: Gather every available source

Collect all email confirmations, blockchain explorers, bank statements, and any saved screenshots. Create a folder or spreadsheet where you can organize them chronologically. This step is tedious but necessary - every piece helps narrow down what happened.

Step 2: Rebuild the timeline

Start with your first deposit to the exchange and your final withdrawal. Use blockchain explorers to find the dates and amounts of crypto transfers. Use bank statements for fiat deposits and withdrawals. Place each confirmed movement on a timeline.

Between deposits and withdrawals, you know you traded, but you don't know exactly when or at what price. You can estimate by looking at the market prices on the dates your deposits arrived and your withdrawals left. This is rough - you'll lose precision on timing and may miss small trades entirely.

Step 3: Decide on a reconstruction method

You have two choices, and the one you pick depends on how much detail you need:

• Summarize by period. If you know you deposited 1 Bitcoin on January 5, withdrew 0.8 Bitcoin on March 10, and made no other movements, you can treat the difference as a single trade or a series of trades that netted to that result. Many tax authorities accept reasonable estimates when records are lost, but check your jurisdiction's rules.

• Use a reasonable estimate for each trade. If you have email confirmations for some trades but not others, you can fill the gaps by assuming you traded at the average daily price on the date of the missing trade. This is less accurate but more defensible than leaving the history blank.

Step 4: Enter the data into your portfolio tracker

Most crypto portfolio tracking software allows manual transaction entry. You will need to input each trade, deposit, withdrawal, and fee by hand, including the date, asset, amount, and price. For trades without a known price, use the estimated price from Step 3 and note in a comment that this is a reconstruction.

What this means for your cost basis

The biggest problem is that without the CSV, you lose the exact cost basis for each trade. If you later sell a crypto that you originally bought on the closed exchange, the gain or loss calculation depends on knowing what you paid. A rough estimate may cause you to overpay or underpay tax.

If the exchange closed years ago and you never filed taxes on those trades, you may need to amend past returns or consult a tax professional. The longer you wait, the harder the reconstruction becomes.

What you should do now for any open exchange

The lesson is straightforward: download CSV exports regularly from every exchange you use, even if you think the exchange is stable. Store them in at least two places - local storage and cloud backup, or an encrypted USB drive. When you close an account, download the CSV before you lose access. A single export covers your entire history on that exchange, and once it is gone, it is gone for good.

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