What if cost or adjusted basis is "missing" from 1099-B form? Should I leave it blank?

No,  The cost basis is the amount that you paid for the investment.  If you leave it blank you will be taxed on 100% of the proceeds.

You will have to determine the basis yourself.  If you have records you should use those.  If not, this tool may help.

You may be able to use Historical Stock Quote Prices - MarketWatch to determine the original value.

To post a correction, leave whatever is in the original entry as it is.  If it is blank, leave it blank. (This will match the 1099-B posting)

1. Scroll to the bottom of your 1099-B entry screen
2. Check the box for The cost basis is incorrect or missing on my 1099-B 
3. On the new screen None of these apply.
4. I know my cost basis and need to make an adjustment.
5. Enter your actual Cost Basis

I had the same issue. I was able to obtain the cost basis and acquisition dates from the financial institution. I followed these steps and selected "something other than a date" then "blank" then "the cost basis is incorrect or missing" and then on the next page, I selected "I know my cost basis and need to make an adjustment" and entered the cost basis. I am still getting an alert that this needs to be reviewed. Should I have entered this in as 1E even though it is not technically on my 1099?

Yes, just enter the acquisition date and cost basis as if they were on the 1099-B.
 

@Lori4100

I sold a mutual fund that I had transferred to Charles Schwab in 2016. Schwab issued a 1099-B that said the cost basis was Missing, but I knew what it was from my Quicken records. However, when I entered the 1099-B in TT and left the cost basis field blank (and said it was incorrect or missing and entered the correct cost basis), TT still kept insisting I review this entry. It was driving me crazy. Finally, when TT did its search for errors at the end, it pinpointed that I must enter something in the 1099-B cost basis field. It would not take the word "Missing" but insisted on a number. When I entered 0, that was acceptable, and the Review button went away.

Will I need to fill out a Form 8949 if we do adjust the cost basis?

No,  The cost basis is the amount that you paid for the investment.  If you leave it blank you will be taxed on 100% of the proceeds.

You will have to determine the basis yourself.  If you have records you should use those.  If not, this tool may help.

You may be able to use Historical Stock Quote Prices - MarketWatch to determine the original value.

To post a correction, leave whatever is in the original entry as it is.  If it is blank, leave it blank. (This will match the 1099-B posting)

1. Scroll to the bottom of your 1099-B entry screen
2. Check the box for The cost basis is incorrect or missing on my 1099-B 
3. On the new screen, None of these apply.
4. I know my cost basis and need to make an adjustment.
5. Enter your actual Cost Basis

Once you enter the 1099-B transaction Form 8949 will automatically create.

Question 1
I followed these instructions:

1. Scroll to the bottom of your 1099-B entry screen
2. Check the box for The cost basis is incorrect or missing on my 1099-B 
3. On the new screen, None of these apply.
4. I know my cost basis and need to make an adjustment.
5. Enter your actual Cost Basis

However I am not prompted for "4. I know my cost basis and need to make an adjustment".

Where can I enter the cost basis?

Question 2: 

My Box 1B says "Unknown" on the 1099B form, however turbotax only has options to put "Various". Do I just leave it blank?

Question3: 
I am unable to clear "Needs Review", how do I clear it? 

1. Please confirm you are following these steps:

1. After choosing "None of these apply," click Continue.
2. The next page says "We notice there's an issue with your cost basis..."
3. Check the box for "I know my cost basis and need to make an adjustment."
4. "Actual cost basis" box appears for you to enter the amount.
5. Continue

2. If Box 1B on your 1099-B has something other than a date but is not blank, choose "Various."

3. Once you are able to complete these steps, the "Needs Review" message should clear.

I'd appreciate additional information from an expert. Please clarify: In my situation, these stocks were part of an ESP. So I didn't spend my own money purchasing them. Do I still put each date they were purchased and the amount of the stock on that day? Some were purchased at different times on the same day so the cost varies, how do I make more than one entry for a day? Thank you.

Yes, enter separate entries for each purchase even if the purchases were done on the same day and even if they were purchased at the same price.  You enter your stock purchases as follows:

1. Log into your account
2. Select Income & Expenses
3. Scroll down the page to Investment Income
4. Select Stocks, Cryptocurrency, Mutual Funds...etc
5. Respond to the questions that appear.  You will see an option to import your transactions; however, continue through the application and you will see an option to I'll type it in myself.  
6. Proceed to enter your information. 

@IImann1059

In my case, my broker (Fidelity) provided me with Form 1099B with box 1e (Cost or Other Bases) with a non-zero value, but with a letter "(e)" suffixed to the value.

When TurboTax imported this data from my broker, it recorded with no value filled in for the "Cost or Other Basis" in its Form 1099B, and in the "Quick Entry Table" for Form 1099B (in TurboTax Premier)

    1. "Basis Reported to IRS" set to "No",  ==> This may be the reason TurboTax left it blank

    2. "Reported on Form 1099B" set to "Yes" ==> So it seems IRS may have this value

My broker also provided "Supplemental Information" with "Adjusted Cost or Other Basis" for those sales with a bigger value than what they had in their 1099B.

So, in this case,

A. should I put any value other than zero in TurboTax's 1099B form for these sales?

B. If so, which of the two values should I put?

    b.1. the value in box 1e in broker-provided 1099B, OR

    b.2 the value in "Adjusted Cost or Other Basis" box in broker-provided "Supplemental Information"

C. If I put zero (or leave it as empty), or the value in above b.1 (i.e., non-adjusted cost basis) in to the TurboTax's 1099B, where can/should I correct (or adjust) the basis? It seems like I can do that through the "Quick EntryTable" for Form 1099B in TurboTax (Premier)? Is that the right place to make the adjustment?

I have to adjust my cost basis for some stocks that were sold. I'm clicking the box on the form that that the cost basis is incorrect on my 1099-B but it is not advancing me to the screen that allows me to put in the correct cost basis. 

Try deleting and re-entering the stock.  To remove such information in TurboTax Online:

1. If you’re on the Hi TurboTax Client, let's keep working on your taxes! screen, click the Pick up where you left off button
2. Click Federal in the left pane, if you’re not already there
3. Click Income & Expenses in the banner
4. Click the Show more dropdown to the right of Investments and Savings
5. Click Start to the right of Stocks, Cryptocurrency, Mutual Funds, Bonds, Other (1099-B)
6. You’ll be able to delete any data previously entered as you proceed through the interview pages
7. Re-enter the stock information

@neen1

@neen1 I had the same problem where the "We noticed there's an issue with your cost basis...Let us know if you'd like to make any changes" part of the interview would not show up. This is how I fixed it:

1. Create an entirely new 1099-B entry in Turbotax via "Add investments".

2. Enter the sale information for the items you need to adjust cost basis (for me, it was three separate line items in my 1099-B; I entered them as three separate items).

3. Check "The cost basis is incorrect or missing on my 1099-B" for each transaction.

4. Next screen: None of these apply (or whatever situation is appropriate for you).

5. "We noticed there's an issue with your cost basis..." should now appear.

6. Enter the correct cost basis.

After this is complete, go back in your original 1099-B that lists the transactions that needed to correct cost basis, and DELETE them so the transactions aren't listed twice in your return.

I believe this is a bug associated with the autoimport functionality. I used the autoimport to import my investment data (can't remember if I did it via uploading the PDF file, or direct download from my instituation; I believe it was the latter).