we are unmarried, but have a joint brokerage account. do we both need to pay taxes? or does only one person need to pay it?
Whose social security number or numbers are on the 1099?
If it is both, then you will need to split the income (which is the correct answer). TurboTaxTom replied to a similar question that may help:
I'll make the assumption that your question is along the lines of "How do I nominee off gains and losses that are all being reported on a 1099-B under my name and social security number?"
The "official IRS-approved" method is to enter the 1099-B as it reads, then enter an "adjustment" (positive or negative) in column (g) of Form 8949 for the other owner's share and a code of "N" in column (f).
You cannot literally do this using the TurboTax interview method, though you can do this if you are using the desktop version and go into Forms Mode. You might not be able to e-file.
You can do a very close approximation, however, if you enter the 1099-B as it reads, then tick the "Add More Details" box and click on the "Start" button. On the next page you tick the first option of "I need to add or fix info about this sale that's on my Form 1099-B." Tell TurboTax that the 1099-B shows an incorrect basis and in the following interview enter the basis figure that gets your personal gain or loss properly stated. TurboTax will put this information into the Form 8949. If basis WAS reported on the 1099-B the code will be wrong - a "B" - and if basis was NOT reported there will be no code. But your income will be properly reported and that's what's really important.
Of course, you are supposed to provide a 1099-B to the nominee and to the IRS, but I expect as a practical matter this doesn't happen too often.