Iowa Code § 422.86 — Payment of estimated tax

A taxpayer required to pay estimated tax under section 422.85 shall pay the estimated tax in accordance with the following schedule: 1. If it is first determined that the estimated tax will be greater than one thousand dollars on or before the last day of the fourth month of the taxable year , the estimated tax shall be paid in four equal installments. The first installment shall be paid not later than the last day of the fourth month of the taxable year . The second and third installments shall be paid not later than the last day of the sixth and ninth months of the taxable year , and the final installment shall be paid on or before the last day of the taxable year . 2. If it is first determined that the estimated tax will be greater than one thousand dollars after the last day of the fourth month but not later than the last day of the sixth month of the taxable year , the estimated tax shall be paid in three equal installments. The first installment shall be paid not later than the last day of the sixth month of the taxable year . The second installment shall be paid on or before the last day of the ninth month of the taxable year and the third installment shall be paid on or before the last day of the taxable year . 3. If it is first determined that the estimated tax will be greater than one thousand dollars after the last day of the sixth month but not later than the last day of the ninth month of the taxable year , the estimated tax shall be paid in two equal installments. The first installment shall be paid not later than the last day of the ninth month and the second installment shall be paid on or before the last day of the taxable year . 4. If it is first determined that the estimated tax will be greater than one thousand dollars after the last day of the ninth month of the taxable year , the estimated tax shall be paid in full on or before the last day of the taxable year . 5. If, after paying any installment of estimated tax, the taxpayer makes a new estimate, the remaining installments shall be ratably adjusted to reflect the increase or decrease in the estimated tax.