If a taxpayer discovers that an original return contains an error in the computation of income or franchise tax, an amended return should be filed. The statute of limitations for filing an amended return is three years from the date the return was filed or was required by law to be filed, whichever is later. Form CD-405 or CD-401S should be used. For tax years beginning after 1998, indicate that the return is being amended by filling in the appropriate circle at the top of the form. For all other years, write AMENDED on the face of the return.