What Is Form 1099-B Used For?
Selling a stock, fund, or other security through a brokerage usually triggers a Form 1099-B the following year, listing the proceeds from every sale along with, in most cases, what was originally paid for the investment.
The short answer
Form 1099-B reports proceeds from broker transactions, such as stock or fund sales, along with cost basis information the broker has on file. Those figures feed into Form 8949 and Schedule D, where capital gains and losses are calculated and categorized before the total moves onto the main return.
What the form actually reports
Each sale during the year typically gets its own line, showing the security sold, the date acquired and sold, the sale proceeds, and, when available, the cost basis, which is generally what was originally paid for the investment plus certain adjustments. The form also indicates whether a transaction was short-term or long-term, which matters because short-term and long-term capital gains are taxed differently, and it separates covered securities from noncovered ones so the reader can see at a glance which figures the broker is standing behind.
Why cost basis reporting isn’t always complete
Brokers are generally required to report cost basis for securities acquired after certain reporting rules took effect, but older holdings, transfers between brokers, or certain types of securities can result in a 1099-B where the basis is missing or marked as not reported. In those cases, the investor is responsible for supplying accurate basis information when filing, using their own purchase records.
How the totals move to Form 8949 and Schedule D
Every transaction on a 1099-B generally needs to be listed on Form 8949, sorted by whether basis was reported to the IRS and whether the holding period was short-term or long-term. Form 8949 totals then flow to Schedule D, which nets everything together into the overall capital gain or loss for the year, a process that also interacts with rules like the wash sale rule, which can disallow a loss if a substantially identical security was repurchased within a set window.
When basis needs adjusting
- Wash sales. A broker may already flag a wash sale on the 1099-B itself, adjusting reported basis accordingly, though not every wash sale situation gets caught automatically.
- Inherited securities. These often use a step-up in basis rather than the original owner’s purchase price, which a broker’s 1099-B may not reflect correctly if the account transferred after death.
- Corporate actions. Stock splits, mergers, or spin-offs can change the basis of affected shares in ways a 1099-B doesn’t always capture cleanly.
Where this leaves you
A 1099-B is a starting point, not necessarily a finished answer — the proceeds are reliable, but the cost basis sometimes needs a second look, especially for older or transferred holdings. Matching the form against personal purchase records before filing is the most reliable way to catch a basis figure that doesn’t reflect what was actually paid, and doing that reconciliation early in the filing season generally leaves more time to track down an old purchase confirmation than waiting until a deadline is close.