Presumptive taxation under section 44AD: taxable business income fixed at presumptive rate; no further business deductions allowed. Income under the presumptive taxation regime is the amount arrived at by applying the presumptive rate to turnover or gross receipts, and that computed amount is the final taxable income with no further business expense allowances or disallowances; Chapter VI-A deductions remain claimable. Depreciation is not separately deductible under the presumptive scheme, but the written down value of assets must be calculated as though depreciation had been claimed and allowed.