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The information transfer is only about a 30 minute process but it is the impact of this change that will be most important. Using an 1120S provides, via schedule K-1 a tax share of the loss to be recognized by the individual shareholders. The 1120, on the other hand, does not provide this loss transfer to the individuals. Thus, all shareholders will need to be notified that their K-1 forms are invalid and they will need to file amended personal returns eliminating any tax benefit they received from the loss and possibly increasing their tax obligation. With an 1120 (C Corp) return the loss is retained by the corporation and used to offset future income. There is an available option, request relief for a late filed election. To do this see that heading in the instructions for form 2553 available at www.irs.gov If you are able to obtain relief it will save you time and the shareholders will save money.