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 Schedule K-1 (Form 1120-S), 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.
Per IRS Shareholder's Instructions for Schedule K-1 (Form 1120-S) Shareholder's Share of Income, Deductions, Credits, etc. (For Shareholder's Use Only), page 3:
Limitations on Losses, Deductions, and Credits
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 limitations, the at-risk limitations, and the passive activity limitations.
To navigate to the Worksheet for Figuring a Shareholder's Stock Basis:
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the webpage or document at the time it is accessed.