S corporation shareholders use Form 7203 to figure the potential limitations of their share of the S corporation’s deductions, credits, and other items that can be deducted on their individual returns. If you have the basis information on your K-1, you should be able to complete the 7203 (You should only have to enter the name of the company). If you are not sure if the business loss is from the S Corp, you will have to contact the S Corp to be sure- it depends on the income reported on your K-1.