S-Corp election approved after already filed 1120 as C-corp

[mhkdgal]

A corporation filed their 2019 taxes in February 2020 on form 1120 as C-corp.  They must have also filed an election to be treated as an S-corp because in Sept 2020 they received the IRS letter stating their election to be treated as an S-corp effective Jan 1, 2019 was approved.

Since their s-corp election was effective Jan 1, 2019, shouldn't the 2019 tax return have been filed on an 1120-S?   Can they leave 2019 filed on a regular 1120, or do they need to go back and amend to an 1120-S?

Thanks in advance!

[IRonMaN]

Filing on an 1120 for an 1120S entity is like filing a 1041 instead of a 1040 and calling it good.  If they really want to be a Sub S when they grow up, they need to file an amended 1120 showing zeroes and and also file an 1120S.

[abctax55]

AND.... the individual's F 1040 (and any state returns) will need to be amended to include the S-Corp K-1 amounts.