Failure to file return incorrect return

1. As soon as practicable after a return required by section 437B.4, subsection 1, is filed, and in any event within three years after such return is filed, the director shall examine the return, determine the tax due if the return is found to be incorrect, and give notice to the taxpayer of the determination as provided in subsection 2. The period for the examination and determination of the correct amount of tax is unlimited in the case of a false or fraudulent return made with the intent to evade any tax or in the case of a failure to file a return. 2. If a return required by section 437B.4, subsection 1, is not filed, or if such return when filed is incorrect or insufficient and the taxpayer fails to file a corrected or sufficient return within twenty days after such return is required by notice from the director, the director shall determine the amount of tax due from information as the director may be able to obtain and, if necessary, may estimate the tax due on the basis of external indices. The director shall give notice of the determination to the taxpayer liable for the tax and to the county treasurers to whom the tax is owed. The determination shall fix the tax unless the taxpayer against whom it is levied, within sixty days after notice of the determination, applies to the director for a hearing. At the hearing evidence may be offered to support the determination or to prove that it is incorrect. After the hearing the director shall give notice of the decision to the person liable for the tax and to the county treasurers to whom the tax is owed. 3. The three-year period of limitation provided in subsection 1 may be extended by the taxpayer by signing a waiver agreement form provided by the department. The agreement shall stipulate the period of extension and the tax period to which the extension applies. The agreement shall also provide that a claim for refund may be filed by the taxpayer at any time during the period of extension.