Rate of interest under IGST Act set with tiered interest and temporary concessional interest windows for eligible taxpayers. Prescribes the rate of interest under the Integrated Goods and Services Tax Act, 2017 read with specified provisions of the Central Goods and Services Tax Act, 2017, setting distinct interest rates for late payment and refund situations and creating taxpayer-class and period-specific concessional interest windows for eligible registered persons, with subsequent amendments modifying applicability and transitional relief.