Your brokerage statement shows the proceeds from a stock sale, but the cost-basis column is blank. If tax software treats that blank as zero, the return may show a much larger gain than you actually had. The missing number is a reason to investigate, not a reason to invent a purchase price.
Cost basis generally starts with what you paid and changes for certain later events. The task is to establish the correct adjusted basis, connect it to the shares sold, and report it in a way that reconciles with the information the IRS received.
Find Out What the Broker Actually Reported
Read the transaction section of Form 1099-B or the substitute brokerage statement. It should indicate whether basis was reported to the IRS. Some holdings are noncovered securities, meaning the broker is not required to report basis for them under the applicable reporting rules. Older purchases and certain transfers can leave gaps in the brokerage record.
A statement may show a basis figure for your convenience while also saying that it was not reported to the IRS. That is different from a covered transaction for which the broker reported a specific basis. Your preparer needs the reporting category as well as the dollar amounts.
Ask the broker whether the figure is missing, awaiting transfer information, or actually incorrect. Request a corrected statement when appropriate, and keep the response. If the broker does not have the history, that does not automatically establish a zero basis. You remain responsible for supporting the amount claimed on the return.
Rebuild the Purchase and Transfer History
Start with original trade confirmations, older monthly statements, and records from any prior broker. For purchased stock, basis generally includes the purchase price and applicable acquisition costs. Match the number of shares sold to the correct purchase lot, because separate purchases of the same stock can have different costs and acquisition dates.
A transfer between your own brokerage accounts ordinarily does not reset the stock’s basis to its value on the transfer date. If the new statement begins with that date, obtain the earlier records. A market price from the day you moved the account is not a substitute for the original adjusted basis.
Check the share-identification method used for the sale. Specific identification has requirements, and you cannot casually choose whichever lot creates the best result after the transaction. First-in, first-out or an eligible average-basis method may apply depending on the asset and elections. Keep the broker’s lot-selection confirmation with your reconstruction.
Include Reinvestments and Other Basis Adjustments
Dividends used to buy additional shares generally create additional purchases with their own basis. If you report the dividend as income but overlook the cost of the reinvested shares, you can overstate the later gain. Review reinvestment statements instead of relying only on the amount of cash you originally deposited.
Stock splits, mergers, spinoffs, and returns of capital can change the calculation. A split generally spreads the existing basis across more shares rather than creating new total basis. Corporate actions can require an allocation among different securities. The company’s shareholder information and the broker’s transaction history may help explain those changes.
Prior wash sale adjustments can also increase the basis of replacement shares in a taxable account. Preserve that history when an account moves. For employee stock, compare payroll and stock-plan documents because compensation income may affect basis beyond what appears on the brokerage statement. Do not assume every zero or low figure is correct for shares received through work.
Use the Correct Form 8949 Treatment
When basis was not reported to the IRS, the correct supported basis generally goes in the cost-or-other-basis field on Form 8949 in the appropriate reporting category. When the broker reported an incorrect basis, the instructions generally require retaining the reported figure and making an adjustment, commonly using code B. Those are different reporting paths.
For a simple illustration, suppose sale proceeds are $6,400, and records establish an adjusted basis of $4,900, with no other adjustments. The gain is $1,500. Treating the missing basis as zero would show a $6,400 gain instead. The correct result depends on records supporting the $4,900, not merely on choosing a lower tax outcome.
Form 8949 generally feeds Schedule D, where capital gains and losses are combined. Review both short-term and long-term sections and any separate adjustments. If you already filed using missing or incorrect basis, compare the corrected calculation with the filed return to determine whether an amendment is appropriate.
Review Special Acquisitions and California Differences
Shares received by gift or inheritance do not always use ordinary purchase cost. Gifted property can require the donor’s adjusted basis and its value when given, while inherited property generally uses a date-of-death value or another permitted valuation. Exceptions and special rules can apply. Obtain donor or estate documentation before assigning a number.
California does not provide the federal preferential rate for long-term capital gains. A separate California capital-gain adjustment can also be necessary when state and federal basis differ. Keep any state basis schedule from earlier returns, especially for transactions with a history of different state treatment.
Local Tax provides tax preparation services in Bellflower and can review the brokerage statement alongside your supporting records. Contact LocalTax with the sale details, original purchases, and transfer history. Resolving the missing basis before filing helps produce a return that reflects the actual investment result.