Aggregating history across multiple exchanges
- Author
- CRYPTO PORT Editorial
- Published
- Updated
- Reading time
- 6 min
In short
Crypto gains are not computed venue by venue and left there: for the same asset, the calculation is generally done across every place you hold it. Adding up each exchange's annual statement does not produce a correct cost basis. Check National Tax Agency guidance on aggregation and consult a tax professional.
Key points
- The calculation is generally per asset, combined across every venue you hold it
- Simply adding each exchange's statement does not give a correct cost basis
- Take care not to double-count transfers between venues as sales
- The first task is enumerating every place you have ever used
Definition
Consolidating history for the same asset spread across several exchanges and wallets into a single calculation, which is necessary for the cost basis to come out right.
People using several exchanges often compute gains venue by venue and add the results. It looks reasonable and it is not correct: the cost basis calculation is generally done per asset, combined across every place you hold it.
Concretely: bitcoin bought at venue A and bitcoin bought at venue B are the same bitcoin. Computing the basis for a sale at A from A's purchases alone leaves out what you hold at B. Neither the total average nor the moving average method can produce an average without the whole set of acquisitions in view, and slicing by venue breaks that premise.
The other practical trap is transfers between venues. Sending the same asset from A to B is a move between places you control, not a sale — but A's history records a withdrawal and B's records a deposit. Processed mechanically, that can become a sale at A and a purchase at B, counted twice. If you use a calculation tool, confirm it recognised the pair as a transfer.
The first task is enumerating every venue you have ever used: not just current ones, but exchanges you left with a zero balance, wallets holding a forgotten small amount, and positions still sitting in DeFi. Miss one and no amount of careful calculation will reconcile. Searching your email for terms like exchange or deposit often turns up accounts you had forgotten.
Once enumerated, export history from each and check that the periods are complete. Then combine, and reconcile against year-end balances. The process is unglamorous, but skipping it makes everything downstream questionable.
Watch out for
- · This page is a general orientation, not tax advice
- · Simply adding each exchange's annual statement does not produce a correct calculation
- · Check National Tax Agency guidance on aggregation and consult a tax professional
Frequently asked questions
What about a venue that has since closed?
Collect whatever survives — deposit and withdrawal records, email notifications from the time, and matching movements in your bank account can all serve as leads. Document how far you could reconstruct and consult a tax professional.