Every 1099-DA reconciliation ends in one of four states per line. The job is to get every line into one of them deliberately, with evidence, instead of discovering the mismatch while you file.
Here is the checklist we built BASISBRIDGE around.
Step 1 — Gather every form and every export
Forms: one 1099-DA per U.S. broker with reportable activity. Brokers issue them early in the year through their tax centers.
Exports: transaction history from every platform and wallet you touched, including ones that sent no form. Foreign exchanges, small platforms, DEX activity and self-custody generally produce no 1099-DA, and those disposals still belong on your return.
Normalize everything to the same shape: date, asset, units, proceeds, fee, wallet/account, and — where you have it — acquisition date and cost.
Step 2 — Fix units before you look at money
Match on asset and units first. Amounts drift for legitimate reasons (fees, rounding, pricing timestamps); unit counts should not. A unit mismatch means a missing transaction, a double-counted transfer, or a split lot — all structural problems that will corrupt any amount comparison you do afterwards.
Step 3 — Classify every line
- Matched — asset, units and proceeds agree within your tolerance.
- Amount differs — the disposal is the same, the money is not. Note the delta and its cause.
- In broker, not in your records — you missed a disposal. Find it.
- In your records, not in broker — expected for non-reporting platforms and self-custody; suspicious if it happened on a platform that did send you a form.
Do not merge these categories. The count in each is the health check on your books.
Step 4 — Investigate the amount differences
The recurring causes, in rough order of frequency:
- Fees. Whether a trading fee reduces proceeds or increases basis depends on how it was charged and reported. Pick a treatment and apply it consistently.
- Pricing timestamps. Your tracker priced the trade at a different second than the broker did.
- Partial fills. One order, several fills, aggregated differently on each side.
- Transfers misread as sales. A move between your own wallets is not a disposal — but a tracker that lost sight of one end of the transfer will book it as one.
Step 5 — Rebuild basis where it is blank
For 2025 sales, brokers were not required to report basis, so most of your lines will need a cost you supply yourself. Work per wallet:
- find the acquisition lot in the wallet where the disposal happened
- record the acquisition date and the cost
- attach an evidence reference — CSV row, bank line, transaction hash
- if the asset arrived as income (mining, staking, airdrop), basis is the fair market value at receipt
An empty Box 1g is not a number to match; it is a number to produce.
Step 6 — Flag what you cannot prove
Some lots will not resolve. Say so explicitly rather than inventing a figure. A basis gap list with three unproven lots and a note on each is a far better position than a clean-looking spreadsheet with three guesses buried in it. Bring that list to your preparer — it is exactly the conversation they want to have.
Step 7 — Produce the working paper and keep it
The deliverable is not a number. It is a document that shows, for each broker line: what the broker said, what your records said, what you concluded, and why. Print it, save it with the year’s tax file, and keep the CSV behind it.
If a question ever arrives, the difference between a bad month and a short letter is whether that document exists.
Do it in the fall, not in April
Two reasons.
First, everything in steps 1–5 depends on data from platforms you might struggle to reach later — some will change export formats, some will shut down, some will lock you out for inactivity.
Second, for sales from January 1, 2026 onward, brokers report basis for covered assets. Your 2027 filing season will be spent explaining disagreements between two reported numbers, not filling blanks. Cleaning the per-wallet history now is what keeps that list short.
The workbench
BASISBRIDGE runs this checklist as a single offline HTML file:
| Tab | What it does |
|---|---|
| Your records | Import or enter your own transactions per wallet |
| Broker 1099-DA | Import the broker’s reported lines |
| Reconciliation | Automatic classification into the four match states |
| Basis gaps | What still has no proven cost, listed for follow-up |
| Summary and memo | CSV export plus a printable working paper |
FIFO, LIFO and HIFO lot methods. Evidence field on every lot. No account, no upload, no installation — and zero network calls, verified in browser testing on Chromium, Firefox and WebKit.
- BASISBRIDGE FREE — 50 rows per table, no cost
- BASISBRIDGE full edition — $49, unlimited rows
A reconciliation working paper is not a tax return and this article is not tax advice. Use it to prepare your records, then work with a qualified professional on the filing.
