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Coinbase missing cost basis: what to collect before a review

A missing cost-basis field is an evidence problem first. It does not, by itself, decide whether a transaction was taxable or how an accountant should file it.

Written by Vitalii Radionov, founder of BasisRestore · For People and accountants working through incomplete Coinbase records. · Updated 2026-09-12

What “missing basis” actually means

Cost basis is the acquisition-side evidence attached to an asset lot. When an exchange cannot match a later sale or conversion to that evidence, the record may show an unknown or estimated basis. A zero or estimated value is a gap to investigate, not a conclusion to copy into a return.

The useful question is: which source can prove when the units arrived, how many arrived, and what acquisition evidence exists? That keeps the review separate from tax advice.

Collect the source records first

Start with original exports and statements. Keep the files unchanged and record where each file came from before making a working copy.

  • Coinbase transaction history or account statement export for the relevant date range.
  • Purchase, deposit, and transfer records that may establish the opening lot.
  • A matching record from another exchange or wallet when the asset moved before the sale.
  • The account timezone, currency, and date range used for every export.
  • A short note for anything you cannot obtain, including the attempted source and date.

Synthetic worked example — no customer data

This two-row path is illustrative only. It uses the canonical Evidence Snapshot fixture and shows where a review must stop; it is not a customer result or a tax conclusion.

Supporting row: coinbase:synthetic:2 is a normalized buy on 2026-02-01 for 1.25000000 BTC; snapshot status confirmed.

Supporting row: coinbase:synthetic:7 is a normalized send on 2026-03-01 for 2.4 ETH; snapshot status unreviewed. Its source transaction type remains +Convert.

Relationship status: proposed. The fixture links the two rows for review only; it is not a matched transfer. The row assets and unresolved source type do not establish a completed movement between accounts.

Open issue: coinbase:synthetic:7 is accountant_review_required; its resolution is still missing. No later sale or return record appears in this fixture, so no acquisition lot path or filing treatment is inferred.

  • Actual supporting rows: 2 (coinbase:synthetic:2) and 7 (coinbase:synthetic:7).
  • Missing evidence: A transaction identifier or receiving-wallet record that resolves row 7's original +Convert type.
  • Missing evidence: A later sale or return record connecting the rows to an acquisition lot.
  • Minimum fields: source row, timestamp and timezone, asset, quantity, account or wallet label, and the source identifier.

Use a review sequence that preserves uncertainty

A defensible reconstruction makes each assumption visible. It should be possible for an accountant to trace a row back to its source without guessing which numbers were invented or rounded.

  1. 01Preserve the original export and calculate a file hash for the working case record.
  2. 02Normalize timestamps and asset symbols without changing the original values.
  3. 03Match deposits, withdrawals, and internal transfers before treating a movement as a disposition.
  4. 04Link a sale or conversion to the best-supported opening lot and record the evidence used.
  5. 05Leave an open item when the evidence cannot support a match; do not silently fill it with a zero basis.

Free qualification and the paid diagnostic are different

The free qualification is a no-upload fit check. It helps decide whether the source, year, volume, and record problem fit the supported workflow; Coinbase's own instructions may be enough when the missing details are known and the case is simple.

The $149 Record Diagnostic is offered only after an accepted scope: one supported Coinbase Retail export, one selected year, and up to 100 sample rows. It provides a written problem map, a reviewed sample, a missing-evidence checklist, and one written next-step recommendation. The delivery date is agreed before payment.

The diagnostic does not include tax advice, filing, full reconstruction, or the complete Evidence Pack. Any larger reconstruction is quoted separately, and a case can end with a clear limitation when the evidence is not sufficient.

Where BasisRestore fits

BasisRestore can review a qualified case using supported Coinbase records, public wallet activity, and documented manual opening lots. The output is a traceable Evidence Pack: reconciled ledger, source map, decision log, and open-items list.

The public qualification form collects metadata only. If a case fits, evidence collection happens through a separate private process. BasisRestore does not request seed phrases, private keys, exchange passwords, or withdrawal-enabled API credentials.

Sources and boundaries

These links are source context, not a substitute for advice from a licensed tax or accounting professional. BasisRestore reconciles records and documents evidence; it does not decide filing treatment.