Under the Income-tax Act, taxpayers can use any of the following accounting methods:
a) Mercantile system: Also known as the accrual basis of accounting, under this method, income is recorded when it is earned, and expenses are recorded when they are incurred, regardless of when cash is received or paid.
b) Cash system: Also known as the cash basis of accounting, under this method, income is recorded when it is received, and expenses are recorded when they are paid, regardless of when they were actually earned or incurred.
c) Either mercantile or cash system whichever is followed regularly: Taxpayers have the flexibility to choose either the mercantile system or the cash system for maintaining their accounts, based on their regular practice.
Therefore, all of the options provided (a), (b), and (c) are permitted accounting methods under the Income-tax Act.