Input tax credit availability clarified for registration changes and composition status, with prescribed reductions and ledger adjustments. Section 18 permits claim of input tax credit for inputs in stock, inputs in semi finished or finished goods in stock, and on capital goods when registration is newly obtained, granted after late application, when a person ceases to pay composition tax, or when an exempt supply becomes taxable; capital goods credits are subject to prescribed percentage reductions. Credit claims are barred after one year from the invoice date; unutilised credits may be transferred on business reorganisation; persons opting into composition or becoming wholly exempt must debit an amount equivalent to attributable credit (reduced as prescribed) to their electronic ledger, with prescribed methods for calculation and adjustment on supply of capital goods.