You move your shares to a new broker, everything looks fine, and months later the cost column reads blank, N/A, or unknown. This explains why the basis went missing, how to get it back, the records to keep, and how to report it so a data gap does not turn into a tax bill.

The transfer itself usually goes smoothly. The positions show up at the new broker, the share counts match, and you move on. The problem surfaces later, often the moment you try to sell, when the cost basis is simply not there. A blank in the cost column, an “N/A,” or a lot marked “unknown.” Nothing looks broken until tax time, and by then the missing number can cost you real money.

Bottom Line First: cost basis goes missing after a transfer for a specific reason, not at random. For covered securities, your old broker has 15 days after the account transfer to send the basis to the new one, and sometimes it arrives late, arrives wrong, or never arrives. For older noncovered lots, brokers were never required to track basis at all, so it often does not transfer and the reporting duty stays with you. The fix depends on which case you are in: call the old broker to have covered basis re-sent, and for noncovered lots, rebuild the basis from your own records before you sell. Do not let a sale post with a zero in the cost column, because a missing basis defaults to counting the entire sale price as gain.

Why the basis is blank, not wrong

A missing basis and a wrong basis are two different problems with two different fixes. Wrong basis means a number transferred but the value or purchase date is off, which we cover in our guide to cost basis that is wrong after a transfer. Missing basis means no number came over at all, so the field is empty. The empty field almost always traces back to one of two causes, and knowing which one you are looking at tells you whether to call the broker or open your own filing cabinet.

The first cause is timing on a covered security. Under the cost-basis reporting rules that took effect for stocks in 2011, your old broker is required to pass basis to the new broker after an account transfer, and it has a window of 15 days to do it. If the basis has not shown up and it has been longer than that, something in the handoff failed and the old broker needs to re-send it.

The second cause is the harder one. Securities bought before the 2011 rules are “noncovered,” meaning brokers were never obligated to track their basis. On a transfer, those lots frequently arrive with no cost information because the delivering broker may not have it in a reportable form. For noncovered lots, the duty to report the correct gain has always been yours, and the transfer just made that obvious.

Covered or noncovered: the one distinction that decides your next move

Before you do anything, sort each affected lot into covered or noncovered, because the two send you down completely different paths.

What you see	What it usually means	Your move
Blank cost on a lot bought in 2011 or later	Covered security; basis did not transfer or arrived late	Call the old broker to re-send it, within and after the 15-day window
Blank cost on a lot bought before 2011	Noncovered security; broker was never required to track basis	Reconstruct the basis from your own records
Lot marked “unknown” or “N/A”	New broker received the shares but no cost data	Confirm covered status, then re-request or rebuild
Basis present but shares show as one big lot	Individual tax lots were merged in transit	Ask the broker to restore lot-level detail before selling

The cost basis is what you paid, adjusted for things like splits, dividends reinvested, and returns of capital. That is the number the empty field is supposed to hold, and it is the number you need to prove a gain or loss when you sell.

Getting covered basis re-sent by the old broker

For covered lots, this is a phone call, not a research project. Contact the delivering broker, the one you left, and ask them to transmit the missing cost basis to the receiving broker for the specific positions. Have your old account number and the transfer date ready. The basis lives with the broker that held the shares when you bought them, so they are the source, and the receiving broker generally cannot invent it.

The IRS explains how basis is determined in Topic No. 703. When a broker cannot supply the number, this is the standard you are held to when you calculate it yourself.

If the 15-day window has passed and nothing has moved, escalate. Ask the delivering broker to open a cost-basis correction or re-transmission request, and get a reference number. Keep the receiving broker in the loop so they know an update is coming and do not lock in a zero when you sell. This is also the moment to check that your individual tax lots survived the move, because a merged position hides the very purchase dates that decide long-term versus short-term treatment.

Rebuilding basis you have to reconstruct yourself

For noncovered lots, or covered ones the old broker genuinely cannot supply, you rebuild the number from evidence. The IRS expects a reasonable, documented effort, not a guess pulled from the air. Start a simple spreadsheet with one row per lot: purchase date, purchase price per share, number of shares, and any adjustments. Then gather the records that support each row.

• Old brokerage statements from the account where you first bought the shares, especially the trade confirmations showing price and date.
• Year-end and monthly statements that show reinvested dividends, since each reinvestment is its own small purchase that adds to basis.
• Corporate action notices for stock splits, spinoffs, mergers, and returns of capital, all of which change the per-share basis.
• Bank or wire records that corroborate the timing of a purchase when a confirmation is lost.
• Historical price data for the exact trade date, used only to estimate when a record is truly gone and you can document why.

One practical note from people who have done this: if you know roughly when you bought but cannot find the exact confirmation, a reasonable reconstruction with supporting records is far better than leaving the field blank. As one tax-forum regular put it, fill in the actual purchase date and price, and keep the proof in case the IRS ever asks. If pulling the records will take weeks and a filing deadline is close, filing an extension and paying an estimate beats reporting a zero basis you know is wrong. If your reconstruction depends on reinvested dividends or fractional lots, our guide to the questions to ask before moving fractional shares and DRIP lots covers what tends to break in transit.

What a missing basis does at tax time

The reason this matters is money, and it shows up on the Form 8949 where you report each sale. If a lot is sold with no basis recorded, the calculation treats your cost as zero, which means the entire sale price is taxed as a gain. Sell $8,000 of stock you actually paid $6,500 for, and a zero basis makes you owe tax on the full $8,000 instead of the real $1,500 profit. That is not a rounding error. It is tax on money you never made.

When the basis was not reported to the IRS, which is normal for noncovered lots, you enter the proceeds and your reconstructed basis yourself and check the box indicating the basis was not reported. For a batch of noncovered lots with different buy dates, you can total the proceeds and basis and enter “various” as the acquisition date. The point is simple: put a real, documented number in the cost column so the gain reflects what you actually earned.

What to watch out for

• Do not sell before the basis is fixed. Once a sale posts with a zero or blank cost, untangling it means an amended return instead of a quick edit.
• Do not assume covered lots are safe. Basis can arrive late or wrong even for post-2011 shares, so verify the number is actually present after the transfer settles.
• Do not overlook reinvested dividends. Every DRIP purchase adds to basis, and leaving them out understates your cost and overstates your gain.
• Do not throw out the old statements. For noncovered lots, those documents are the only proof you have, and no broker will reproduce them for you.

This article is for general information only and is not financial, investment, or tax advice. Cost-basis rules, broker procedures, and reporting requirements can change, and individual situations differ, so check current official sources such as the IRS and confirm with a qualified tax professional before filing or making decisions about your accounts.

Frequently Asked QuestionsWhy is my cost basis missing after a brokerage transfer?

Usually one of two reasons. For securities bought in 2011 or later, the old broker is required to send basis to the new broker within 15 days of the transfer, and that handoff can fail or run late. For shares bought before 2011, they are noncovered, so brokers never had to track basis and it often does not transfer at all. Which case you are in decides whether you call the broker or rebuild the number yourself.

How do I get the missing basis added at the new broker?

For covered lots, contact the broker you transferred away from and ask them to re-transmit the cost basis for the specific positions, with your old account number and the transfer date ready. They hold the original data. If the 15-day window has passed, request a formal cost-basis correction and get a reference number, and tell the new broker an update is coming so they do not settle a sale with a zero cost.

What if I cannot find records for old shares?

Reconstruct a reasonable basis from whatever you can find: old statements, trade confirmations, reinvested-dividend records, and corporate-action notices, supported by historical price data for the trade date when a record is truly gone. The IRS expects a documented, reasonable effort. A well-supported estimate beats reporting a zero basis, which would tax your entire sale price as gain.

What happens if I just report a zero cost basis?

You almost certainly overpay. A zero basis means the full sale price is treated as profit, so you pay tax on money that was your original investment, not a gain. If you paid $6,500 for stock you sold for $8,000, a zero basis taxes the whole $8,000 instead of your real $1,500 gain. Put a real, documented number in the cost column instead.

Does transferring shares between brokers trigger a taxable event?

Moving shares in kind from one broker to another is not itself a sale, so it does not trigger tax on its own. The tax consequences come later, when you sell, which is exactly why a missing or wrong basis matters. The transfer is tax-neutral; the recordkeeping around it is what protects you at filing time.

What To Know

• Missing basis after a transfer is different from wrong basis: the field is empty, not incorrect, and the fix depends on why.
• Covered lots bought in 2011 or later should transfer within 15 days; if they do not, the old broker re-sends the number.
• Noncovered lots bought before 2011 often carry no basis, and reconstructing it from your records is your responsibility.
• A missing basis defaults to a zero cost, which taxes your entire sale price as gain.
• Fix the basis before you sell, and keep old statements and reinvestment records as proof.

Practical Takeaway

Treat a blank cost column as a stop sign, not a formatting quirk. Sort each affected lot into covered or noncovered first, because that single distinction decides whether you pick up the phone or open your records. For covered lots, call the delivering broker, confirm the 15-day handoff, and get a reference number if it failed. For noncovered lots, build a lot-by-lot spreadsheet from old statements, trade confirmations, and reinvested-dividend records, and document your reasoning where a receipt is gone. Then, before you sell anything, make sure a real number sits in the cost field, so your gain reflects what you actually earned rather than the whole sale price. For more on brokerage moves and taxable-account decisions, browse Venture-Lab’s Investment coverage.