A missing cost stays missing. BasisFix will not invent a price to finish the total.

Not tax advice · reviewed 25 October 2026

Missing basis and lost lots

Gain is proceeds minus basis. If the basis was never in the file, the gain is unknown. BasisFix flags that hole and refuses to paper over it. The sheet you export is a review with a tax pro, and a row with Included in totals set to no is not part of the short-term or long-term number.

How a hole opens

A deposit or a receive with no USD amount, and no matched send from another file you imported.
An income row with no fair market value. The lot opens, and the income total skips it. See bitcoin interest income.
A sale that needs more coins than the account has, or that consumes a lot with no basis.
A non-USD quote. This build has no exchange rates, so those lots have no USD basis.

An incomplete sale is still shown on the worksheet. Known lots it validly consumed stay closed, so they are not sold a second time. The unknown slice is what drops out of the total.

What the worksheet will not substitute

Zero. That reports every dollar of proceeds as gain. It is a guess with a direction.
Today’s price, or the price on the deposit date, looked up from a feed. There is no price feed.
River’s Cost Basis column. Even when the CSV contains one, BasisFix does not read it. See River’s Cost Basis column.
A sale, invented from a send. An unmatched or ambiguous send stays in the source account. It is not proceeds.

Ways to close the hole

Import the earlier buy. A River withdrawal plus a later wallet file can be one lot when the transaction id matches, or when there is exactly one same-asset, same-quantity candidate inside three days and the accounts differ. The original acquisition date moves with the coins. The holding period does not restart.
Add a generic row whose quote_amount is the USD cost you can support, and whose timestamp is the real acquisition time. You are asserting that number. BasisFix will believe the cell.
Leave the row excluded and hand the warning to a tax pro. That is a complete use of this worksheet.

Duplicates are a different flag. The same external id, asset, direction, and quantity keeps one row, preferring a row that has a USD amount. A second copy of a Cash App buy is not a second lot.

Lost keys are outside the worksheet

BasisFix does not turn a wallet you cannot open into a deduction, a sale at zero, or a worthless-asset claim. Those are legal characterizations this build does not attempt. Tell a preparer what you can still prove you bought, and what you can no longer move. Do not “solve” it by typing a sale that did not happen.

Questions

Should I use zero when the cost is missing?

Not and not as a default. Zero basis reports the entire proceeds as gain. The worksheet leaves the disposal out of the gain total and marks Included in totals as no.

Does an unmatched withdrawal become a sale?

No. The lots stay in the account that sent them, and the worksheet warns you. A matching receive, by shared transaction id or the only same-amount candidate within three days, carries basis and the original date across.

Will the worksheet deduct coins in a lost wallet?

No. It does not classify theft, a casualty, or a worthless position, and it does not know whether a deduction is available. That decision stays with a tax pro.