Cenvat credit apportionment requires a single annual option and excludes credit for exclusively exempted use of inputs. Cenvat credit is disallowed for inputs and input services used exclusively for exempted outputs, while credit on inputs and input services used for both dutiable and exempted outputs is allowed. Assessees not maintaining separate Cenvat accounts must elect one comprehensive apportionment option for the whole financial year: a percentage-based payment of the value of exempted outputs or payment equal to the attributable Cenvat credit, computed excluding exclusively used inputs and certain excluded input services. Attribution must follow actual consumption supported by records and a professional certificate; export of service without tax is not treated as exempted service and ISDs cannot opt for these schemes.