More information is needed to answer your question. Tax issues such as these are very fact specific and the answer may often turn or be effected but what may seem to be a slight technicality. First, we need to be certain that the account receivable was properly contributed to the corporation and the contribution complied with IRC section 351. I would also be concerned if the debt was owed to you by a family member. Was there a business purpsoe for the contribution. What were the payment terms and was the debtor current with paymens at the time the contribution was made to the corporation. If the item was a valid account receivable or an amount that you had the right to receive and that account was still collectible at the time of contribution and had value, then there may be a basis for a nonbusiness bad debt deduction. This issue should be reviewed carefully by your tax preparer or professional.
You say that you have a "personal debt." Does this mean the loan was personal in nature? Or do you mean the debt was a business debt owed to you personally?
As far as any money you loaned the S-corp, you are not going to be able to write that off unless the S-Corp can never repay you the loan. This is unrelated to any personal loan you have. If the S-Corp loaned money for a business or investment purpose to another entity, and this is noncollectable now, then the entity can take a loss.
The personal debt is a separate issue. What was the loan for? Was it business or investment? Was it a loan to a friend or family member? Is there a written agreement? Was interest collected on the loan as if it were an arms-length transaction? Or were payments constantly forgiven as they never would have been in an arms-length transaction?
As the previous attorney states, there are many factors that determine whether this can be deducted as a loss. But it is somewhat implied that the debt is personal in nature, so I am going to say that if that is the case, it will likely not be deductible.
As you can see from the detailed nature of the answers that you have received above, though your question seems simple on its face, there are multiple aspects to the question all of which could change the potential answer.
I think this is a situation where you are well advised to sit down with a CPA or tax attorney familiar with corporate tax returns. You need to give them the opportunity to examine all of the paperwork (including corporate records) that relate to this particular debt. If you get this wrong, you could end up in an audit owing taxes, penalties and interest to the Internal Revenue Service (which is definitely a bad thing). Invest your time in consulting with an expert.
I understand that this is not an answer to your question in a yes or no fashion, but I hope these thoughts are helpful.
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The corporation can write it off but the question is probably really whether it (meaning you) can take it as a tax deduction. I doubt that contributing a personal loan to a company converts it to a business loan and, therefore, the bad debt cannot be deducted from ordinary income. It may be deductible from capital gains income the corporation receives just as it would be for you if you still held it. Your basis in the company should not change because the debt became worthless any more than if you had contributed a vehicle that had been destroyed. Of course, the assets of the company will be adjusted in the write off so the capital in the company will go down and the amount of taxible income to you could increase as a result (your return of capital will end sooner). There are other complications that would need to be considered, as the other counsel have indicated. And if you have other shareholders another host of problems would come up. See a tax attorney.