had lend 6k, for a return of 30% over awhile, however, when the time came, I was only returned 2k (principle), I had still lost 4k excluding the interest.
It depends. The debt must have been a bona fide loan—you gave the money with every expectation of being repaid. If you charged interest, and the borrower signed a promissory note, this provides a good indication that you expected to get your money back.
The actual task of reporting a bad debt is relatively simple. The steps are:
Form 8949 (Sales and Other Dispositions of Capital Assets) records the details of your capital asset (investment) sales or exchanges. Part I of the 8949 shows the short-term transactions (held less than a year) and Part II has the long-term transactions.
When you enter investment sales or exchanges from Form 1099-B or 1099-S in TurboTax, we'll automatically fill out Form 8949 and transfer the info to Schedule D. You don't need to fill out the 8949 yourself. See this article for more information about when you need to fill out or mail in Form 8949.
The IRS also requires that you attach a bad-debt statement to your tax return, explaining the details of the loan you made. You must deduct a bad debt in the year it becomes worthless. If you realize you could have reported and taken a deduction for an unpaid debt years ago but didn't, you generally have only three years to amend your return in order to claim it on your tax return.