Please see this answer from @AnnetteB6.
In order to claim home office expenses as a trader, you will need to be using a CD/downloaded version of TurboTax because there is an entry that will be required to be entered directly on a worksheet in Forms Mode.
If you have not elected and submitted the Mark-to-Market (MTM) accounting method, then go to Forms Mode to view your Schedule D. Line 16 of Schedule D will show the overall gain or loss being reported on your return. If you did not report any transactions during the year as an ‘investor’ and Schedule D shows only your gains/losses from being a ‘trader’, then line 16 is the amount you use in the home office instruction below. Otherwise, you must do some math outside of your return to determine only the overall gain/loss from transactions associated with your business as a ‘trader’. Transactions as an investor (for example, selling a long-term holding) cannot be considered to be income associated with your business as a trader.
If you have elected and submitted the MTM accounting method, then go to Forms Mode to view your Form 4797. If you have no other items reported on Form 4797 except for your trader activity, then the ‘trader’ gain is the amount from line 18b. Otherwise, you will need to calculate the total gain for your trader activity only to use in the home office instruction below.
All business expenses will contribute to Schedule C showing an overall loss since the income from trading is not reported directly on Schedule C. With an overall loss on Schedule C, no self-employment tax will be imposed.
