Section 2(11)(a) in The Bengal Agricultural Income-Tax Act, 1944
(a)the twelve months ending on the 31st day of March next preceding the year for which the assessment is to be made, if the accounts of the assessee have been made up to a date within the said twelve months in respect of a year ending on any date other than the 31st day of March, then at the option of the assessee the year ending on the day to which his accounts have been so made up;