Hello,

I had some stocks from a company which was sold and I gained around $40,000, which are a long term gain. I am being told that I have to return money to the IRS now, before the end of the year, because it is not good to owe the IRS too much at the end of the year and I may get a fine. Is this true and what form(s) should I fill to return the money? How much is the tax for this money?

Thanks,
Ivan.

Read about estimated tax payments here
Your U.S. Tax Return: Tax Filing by Self Employed Sole Proprietor or Independent Contractor

Ivan:

A $40K capital gain DOES require that you make a quarterly estimated tax payment, which would be due on 15 September 2008 for a sale made from 1 June to 31 August 2008.

You would prepare and file Form 1040-ES, and mail the payment with the voucher by 15 September 2008.