As stated above in the matching concept, the revenue generated in the accounting period is considered and the expenditure related to the accounting period is also considered. Based on the accrual concept of accounting, if we sell some items or we rendered some service, then that becomes our point of revenue generation irrespective of whether we received cash or not. The same concept is applicable in case of expenses. All the expenses paid in cash or payable are considered and the advance payment of expenses, if any, is deducted.
Most of the professionals use cash basis of accounting. It means, the cash received in a particular accounting period and the expenses paid cash in the same accounting period is the basis of their accounting. For them, the income of their firm depends upon the collection of revenue in cash. Similar practice is followed for expenditures. It is convenient for them and on the same basis, they pay their Taxes.