Section 280-RICR-20-25-5.6 - Declaration - Due Date - Payment - InterestA. Every corporation is required to file estimated taxes if their estimated liability for the taxable year can reasonably be expected to exceed five hundred dollars ($500) pursuant to R.I. Gen. Laws §44-26 - 2.1(a). 1. For Calendar Year taxpayers, four (4) equal installments of twenty-five (25%) percent are due on April 15th, June 15th, September 15th, and December 15th of the taxable year.2. For Fiscal Year Taxpayers, four (4) equal installments of twenty-five (25%) percent are due on the 15th day of the fourth, 15th day of the sixth month, 15th day of the ninth month, and 15th day of the twelfth month of the taxable year. 3. Every corporation required to make estimated tax payments shall report such payments on Rhode Island's Form BUS-EST.B. If multiple payments are being made for different obligations with one check (for example, an extension and an estimated tax payment), the appropriate separate coupons shall accompany the payment(s). C. If the required estimated payments are not made, then underestimated interest shall be calculated and reported on Form RI-2220 when filing the annual return.D. In the event the estimated tax liability increases, an entity may file an amended estimated declaration and shall file and pay an additional amount at the time of the amended declaration. However, underestimating interest may still be assessed.280 R.I. Code R. 280-RICR-20-25-5.6