kooltrader, It is not simply a matter putting a number on line #13 vs. line #12. The values on these lines tie into amounts on Sch C and Sch D, which in turn must be prepared correctly and tie back to their source documents.Quote from kooltrader:
It looks to me that the mistake I made was writting down the profit on 1040 on line 12 instead of line 13, which requires me to pay self-emplyment tax.
If you are a bona fide "trader" for IRS purposes then there are tax deductions allowable, but you need to know the law and how to apply it and then report the results properly on your tax return. If you are not "in the business" enough to qualify as a trader, then Sch A is used rather than Sch C.
In fact the trading gains for traders as well as for investors are exempt from self-employment tax, per a long history of statutary law. Dealers are subject to S/E and they use Sch C to report the gains, unlike traders or investors.