A missing key is not a proceeds number, and it is not an automatic deduction.
Not tax advice · reviewed 25 October 2026
Lost or stolen bitcoin
People lose keys, and people get coins taken. Whether that is a theft loss, a casualty loss, a capital loss, or no deduction at all is a question BasisFix does not answer. It does not apply a statutory limit, and it does not describe one. The worksheet will not turn the story into a zero-proceeds sale. It is a review with a tax pro.
What the engine will and will not close
- A send that does not match a receive stays in the source account. Lots are not consumed to manufacture a disposal. See self-transfers are not sales.
- There is no “stolen” or “lost” transaction type. Adding one would still not compute a deduction.
- A sale with unknown basis is excluded from the gain total. That is the missing-cost case, explained on missing basis and lost lots. It is not a theft deduction.
- Do not type zero proceeds to force the basis out as a loss. BasisFix will believe a sale you enter. It should only be a sale if that is the transaction you and your preparer are reporting.
Keep whatever evidence you have: the exchange ticket, the wallet record, the date you last controlled the coins. None of that is uploaded here. The calculator and the reconciler both stay in the browser.
Questions
Does a lost wallet become a deduction here?
No. BasisFix does not compute a theft loss, a casualty loss, or a zero-proceeds sale. Those questions are outside the worksheet. A preparer decides whether any deduction exists.
What happens to the lots if the coins are gone?
An unmatched send stays in the source account. The lots are not closed and they are not given a gain of the full basis. If you no longer have the keys, the records still need a decision you make with a preparer, not a silent zero.
Is a missing cost the same as a lost coin?
No. Missing basis means the coins may still be there and the USD cost is unknown. A lost or stolen coin is a different problem. Both are left unresolved rather than filled with zero. The missing-basis guide covers the first one.