How to Report 1099-B Undetermined Term Transactions

If your 1099-B shows an “undetermined” holding period, you have to figure out whether the sale was short-term or long-term, supply the cost basis yourself, and report the transaction on Form 8949 before the totals carry to Schedule D. This is how to report 1099-B undetermined term transactions correctly: identify the acquisition date, calculate the basis, classify the holding period, and use Box B or Box E on Form 8949 with an adjustment code if the basis your broker reported is blank or wrong. The classification is not a formality. A short-term gain is taxed at your ordinary income rate, which can reach 37%. A long-term gain caps out at 20% and can be as low as 0%.

Why the Term Shows as Undetermined

Form 1099-B is what brokers file to report the proceeds from selling stocks, bonds, and other securities to you and to the IRS.¹ Box 2 is where the broker checks short-term, long-term, or ordinary.² When that box is blank or the statement says “undetermined,” the broker did not classify the holding period at all.

Look at Box 5. If it’s checked, the security is noncovered, and the broker was never required to report the cost basis (Box 1e), the acquisition date (Box 1b), or the type of gain or loss (Box 2).² Only the gross proceeds come from the broker. Everything else is on you.

A security is covered if you acquired it on or after the date basis reporting became mandatory for its type:³

Most corporate stock: on or after January 1, 2011
Mutual fund and dividend reinvestment plan shares: on or after January 1, 2012
Other specified securities such as bonds and options: on or after January 1, 2013

Anything bought before those dates is noncovered. Shares that arrived through complex corporate events such as mergers or spin-offs can also be treated as noncovered, even when the original purchase was recent, because the broker’s system may not have a clean basis to trace.

What You Need to Reconstruct

Three pieces of information turn an undetermined term line into a reportable transaction: the acquisition date, the cost basis, and the sale date.

Acquisition Date

Start with the brokerage where you originally bought the shares, even if they’ve since moved to another firm. Old trade confirmations, monthly statements, and annual summaries typically list the transaction date and price. If the shares were transferred between brokers, the receiving firm sometimes carries the original acquisition date on the transfer statement, but for noncovered securities that isn’t guaranteed.

The holding period begins the day after you acquired the asset and ends on the day you sold it.⁴ Held one year or less is short-term. Held more than one year is long-term. A share bought March 15, 2009 and sold March 16, 2010 is long-term by a single day.

Cost Basis

Cost basis is generally what you paid for the security plus any commissions or transaction fees on the original purchase. Buy 100 shares at $25 with a $10 commission, and your basis is $2,510. Overstating basis understates your gain and can draw penalties. Understating basis makes you overpay.

Sale Date and Proceeds

The sale date is in Box 1c of the 1099-B and the gross proceeds are in Box 1d.² Check them against your own records, then use the acquisition and sale dates together to place the transaction in the short-term or long-term bucket.

Basis Adjustments That Change the Number

Noncovered shares are disproportionately affected by events that push basis away from a simple purchase price. If any of these apply, the number you enter on Form 8949 is not what you originally paid.

Inherited Shares

Basis in inherited securities is generally the fair market value on the date the original owner died, not what they paid.⁵ This stepped-up basis can shrink or erase a gain. The executor may have elected an alternate valuation date six months after death, so check the estate tax return if one was filed.

Gifted Shares

For gifts, the rule splits. If you sell at a gain, your basis is the donor’s original basis. If you sell at a loss, your basis is the lower of the donor’s basis or the fair market value on the date of the gift.⁶ If the sale price falls between those two figures, there is no gain and no loss. You may also be able to add a portion of any gift tax the donor paid.

Stock Splits and Corporate Actions

A stock split spreads your existing basis across more shares. Own 100 shares with a $1,000 total basis, and after a two-for-one split you have 200 shares at $5 basis each with the same $1,000 total.⁷ If you bought lots at different prices, allocate the split lot by lot rather than averaging. Spin-offs work similarly, with a portion of the parent’s basis allocated to the new company’s shares based on relative market values.

When the Records Are Gone

Old purchases, defunct brokerages, and lost statements can make an acquisition date and original price genuinely unknowable. There are still options, none of them as good as the original paperwork.

Contact the brokerage, or its successor if the firm merged or was acquired. Many keep records further back than expected. The company’s transfer agent may have a record of when you first appeared as a registered shareholder. Historical price data can help reconstruct what you likely paid on a given date if you can narrow the purchase window.

If nothing turns up, reporting a zero basis is the safest position against penalty, but it means you pay tax on the full proceeds as gain. Some taxpayers reconstruct a reasonable basis from historical prices and approximate dates. Whichever route you take, document the method. The IRS can challenge a claimed basis, and forgetting is not a defense.

Filling in Form 8949

Form 8949 is where each sale gets its own row and where you connect the broker’s proceeds to the gain or loss you calculated.⁸ Part I is for short-term transactions, Part II for long-term. Once you’ve classified the undetermined term sale, it lands in one part or the other.

The Right Checkbox

For an undetermined term transaction on a noncovered security where you got a 1099-B but the basis was not reported to the IRS, check Box B if short-term or Box E if long-term.⁸ That combination tells the IRS a 1099-B exists and the basis on it was not reported to them, which is the standard posture for noncovered shares.

Do not use Box C or Box F. Those are for sales that never generated a 1099-B at all. Form 8949 also has boxes G through L for digital asset transactions reported on Form 1099-DA; those don’t apply to traditional securities.⁹

The Columns

Column (a): description of the property, such as “100 sh XYZ Corp”
Column (b): the acquisition date you researched
Column (c): the sale date from Box 1c of the 1099-B
Column (d): proceeds from Box 1d
Column (e): your cost basis, including commissions and fees from the original purchase
Column (h): gain or loss, calculated as column (d) minus column (e), adjusted for anything in column (g)

The Adjustment Code

If the 1099-B shows an incorrect basis, including a zero or blank basis, put Adjustment Code B in column (f).¹⁰ For a Box B or Box E transaction you enter the correct basis directly in column (e) and put zero in column (g); the code signals that you’re supplying the number the broker didn’t.

Each undetermined term transaction gets its own row. You can’t combine multiple sales on one line except under narrow exceptions for identical securities sold on the same date at the same price.

Carrying Totals to Schedule D

Form 8949 totals flow to Schedule D, where all your capital gains and losses come together.¹¹ Short-term totals from Part I of Form 8949 go to Part I of Schedule D. Long-term totals from Part II go to Part II.

This is where the holding period pays or costs you. Short-term gains are taxed at your ordinary income rate, which runs from 10% to 37%. Long-term gains are taxed at 0%, 15%, or 20% depending on taxable income. Getting the classification right is the whole reason the earlier research matters.

Capital losses first offset gains of the same type: short-term against short-term, long-term against long-term. Any remaining net loss then offsets gains of the other type. Whatever is left after all the netting can offset up to $3,000 of ordinary income, or $1,500 if you’re married filing separately.¹² Anything beyond that carries forward indefinitely and keeps its short-term or long-term character when you use it later.

Wash Sales the Broker Didn’t Track

If you sold a noncovered security at a loss and bought substantially identical shares within 30 days before or after the sale, the wash sale rule disallows the loss.¹³ The disallowed amount adds to the basis of the replacement shares, deferring the loss until you sell those without triggering another wash sale.

For noncovered shares, the broker likely didn’t flag the wash sale. You have to identify it, adjust the replacement shares’ basis, and report the disallowed loss on Form 8949 with the right adjustment code. If the replacement shares are also noncovered, the layered adjustments can compound quickly.

Worthless Securities

If a noncovered security became completely worthless during the tax year rather than being sold, the IRS treats it as sold on the last day of that year for zero proceeds.¹⁴ You still classify the holding period. The deemed December 31 sale date means most worthless securities produce long-term losses, provided you acquired them more than a year earlier.

Penalties and Recordkeeping

Underreporting a gain or overstating basis on an undetermined term transaction can draw the accuracy-related penalty: 20% of the underpaid tax if the IRS finds negligence or a substantial understatement.¹⁵ For individuals, a substantial understatement means the tax was understated by the greater of 10% of the correct tax or $5,000. Interest runs on any underpayment from the original due date and compounds daily. Showing reasonable cause and good faith can head off the penalty, which is why documenting how you arrived at your basis and holding period matters.

Keep records for securities until the statute of limitations expires for the year you sold them, generally three years from filing.¹⁶ If you underreport gross income by more than 25%, the IRS has six years. If you never file or file a fraudulent return, there is no limit. For noncovered shares you still hold, hang on to the records that prove your acquisition date and original cost basis for as long as you own the shares, then add the limitations period after you sell. Losing those records while you still hold the shares is how undetermined term transactions get made in the first place.

1
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