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What to do if I forgot to check final K-1 box on form 1120-S and 2019 was my last year of operation.
Was the final return box checked on your 1120-S? If you prepared your 1120-S with TurboTax Business, then the final K-1 box on your K-1 should also have been checked.
If you simply forgot to indicate the K-1 was final in a personal version of TurboTax, then you might need to file an amended return. You should save your original .tax2019 file on different media, start an amended return, and check the "This S corporation ended in 2019" box in the K-1 section of the program.
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