Tonnage tax charter-in limit restricts chartered net tonnage; exceeding triggers loss of tonnage-tax benefits for the year. Companies under the tonnage tax scheme must not charter in more than forty-nine per cent of the average net tonnage of qualifying ships in any previous year; the average is computed as prescribed in consultation with the Director General of Shipping. Exceeding the limit in a year requires computing total income as if the tonnage option were not in effect; exceeding in two consecutive years terminates the option from the beginning of the following previous year. 'Chartered in' excludes vessels on bareboat charter cum demise terms.