While the at-risk limitations are calculated on IRS Form 6198
At-Risk Limitations and the passive activity limitations are calculated on IRS Form 8582 Passive Activity Loss Limitations, there is not an IRS form for the potential limitations on the amount of corporate losses that you may deduct based on your basis in the corporation. You would need to enter only the loss allowed on Line 1 of the Schedule K-1, and then manually track the shareholder basis and the amount not allowed in the current year which could be carried forward to the time when the basis in the S Corporation allows the loss to be taken.
IRS Shareholder's Instructions for Schedule K-1 (Form 1120S), page 2:
There are potential limitations on corporate losses that you can deduct on your return. These limitations and the order in which you must apply them are as follows: the basis rules, the at-risk limitations, and the passive activity limitations.
Each of these limitations is discussed separately in the instructions.
To navigate to the Worksheet for Figuring a Shareholder's Stock Basis:
NOTE: If, after you click Print in Step 5 above, you are directed to the Payment Option screen, you will need to process the product fees prior to printing.