HI, would it be possible to use turbotax to make an estimated tax payment for capital gains from stock sales in 2023? This would be separate from my 2023 tax return.

You cannot make an estimated tax payment through TurboTax. You can make the payment using Direct Pay on the IRS web site.

Thanks for the info, that helps. Does the IRS need any other documentation or forms filled out that need to be sent to them to document the transaction(s)? 

No.  You just pay the estimated payment.  You should get a 1099B for the sales in January or February to enter into your tax return.  You will need to use the Premium version to enter investments.   You also need to enter all the tax estimates you paid, so keep track of the date you paid it and the amount to get credit for it.

To enter Federal or State Estimated Taxes Paid, including a state estimated payment made in January for the prior year, go to

Federal on left or at top (Personal for Home & Business)

Deductions and Credits at top

Then scroll way down to Estimates and Other Taxes Paid

Estimated Taxes - click the start button