I HAVE SOLD SOME STOCKS THAT I HAVE NO INFO ABOUT COST BASIS. CAN I REPORT COST BASIS ZERO?

[MinhT1]

You would have to find, estimate or guess your cost basis by searching past values for these stocks.

You can of course report a 0 cost basis, but then you would be inflating your capital gains and pay more capital gain taxes.

[Khomein]

ONE OF THE STOCKS HAS BEEN CREATED ON 2024 FROM THE MERGE OF 4 OTHER COMPANIES ON APRIL 2024, I FOUND HISTORICAL DATA FROM YAHOO FINANCE. CAN I USE THIS PRICE AS THE BASIS? 

[Khomein]

IF THE COST BASIS I REPORT IS HIGHER THAN IRS CALCULATIONS, WHAT WOULD BE THE CONSEQUENSES?

[MarilynG1]

Yes, you can use that value as your Cost Basis.  Keep documentation showing the amount you used with your tax files. 

Here's more info on How to Find a Stock Cost Basis.