Here is the “Overall FTC Limitation Formula.”
FTC Limit (Line 21) = U.S. Tax Liability (Line 20) x Foreign Taxable Income (Line 17) Worldwide Taxable Income (Line 18)
Notice that if Line 17 is zero, The FTC Limit would be zero. If Line 17 is negative, the FTC Limit would be negative which is meaningless. Since there is no FTC Limit, there can be no Foreign Tax credit. For TY2018, you could not use your carryforwards from previous years and cannot use a carryback from TY2019.
