§ 145.801 RSMo — Claims for credit or refund — limitations on time allowed for filing and amount — amended return, time limited — interest on refund or credit ceases, when

1. A claim for credit or refund of an overpayment of any tax imposed by sections 145.011 to 145.995 shall be filed by the taxpayer within three years from the time the return was filed or two years from the time the tax was paid, whichever of the periods expires the later; or if no return was filed by the taxpayer, within two years from the time the tax was paid. No credit or refund shall be allowed or made after the expiration of the period of limitation prescribed in this subsection for the filing of a claim for credit or refund, unless a claim for credit or refund is filed by the taxpayer within the period.

2. If the claim is filed by the taxpayer during the three-year period prescribed in subsection 1, the amount of the credit or refund shall not exceed the portion of the tax paid within the three years immediately preceding the filing of the claim plus the period of any extension of time for filing the return. If the claim is not filed within the three-year period, but is filed within the two-year period, the amount of the credit or refund shall not exceed the portion of the tax paid during the two years immediately preceding the filing of the claim. If no claim is filed, the credit or refund shall not exceed the amount which would be allowable under either of the preceding sentences, as the case may be, if a claim was filed on the date the credit or refund is allowed.

3. If pursuant to subsection 5 of section 145.711 an agreement for an extension of the period for assessment is made within the period prescribed in subsection 1 of this section for the filing of a claim for credit or refund, the period for filing a claim for credit or for making a credit or refund if no claim is filed, shall not expire prior to six months after the expiration of the period within which an assessment may be made pursuant to the agreement or any extension. The amount of the credit or refund shall not exceed the portion of the tax paid after the execution of the agreement and before the filing of the claim or the making of the credit or refund, as the case may be, plus the portion of the tax paid within the period which would be applicable under subsection 1 of this section if a claim had been filed on the date the agreement was executed.

4. If a taxpayer is required by section 145.601 to report a change or correction which is treated in the same manner as if it were an overpayment for federal estate tax purposes, an amended return or a claim for credit or refund of any resulting overpayment of tax shall be filed by the taxpayer within one year from the time the notice of such change or correction or such amended return was required to be filed with the director of revenue. If the report or amended return required by section 145.601 is not filed within the ninety-day period therein specified, interest on any resulting refund or credit shall cease to accrue after the ninetieth day. The amount of such credit or refund shall not exceed the amount of the reduction in Missouri estate tax attributable to the effect of the issues on which the federal change or correction or the items amended on the taxpayer's amended federal estate tax return are based.