To validly record this entry and claim ITC, you must possess a proper tax invoice from the supplier that includes their GSTIN, the HSN/SAC code of the items, and the specific IGST amount charged. Software Recording (e.g., TallyPrime / Tally.ERP 9) How to pass accounting entries under GST - ClearTax

IGST applies only when the "Place of Supply" is in a different state from the buyer's registered location.

IGST is calculated by applying the relevant tax rate (e.g., 5%, 12%, 18%, or 28%) to the total taxable value of the goods. For imports, it is calculated on the value including Basic Customs Duty (BCD) .