There are two provisions oft confused:-
Sec 44AD - Business Income (other than professional) Minimum 8% of TO (6% if receipts are through banking channel) has to be declared as profit (or higher profit if the actual is more than 8%/6%). persons earning commission/brokerage are not eligible for this presumptive scheme. Once opted for an AY, the assessee must declare profit under 44AD for continuous 5 AYs. If opted out in between, then he shall not be eligible to opt in again for next 5 AYs and he shall be subject to tax audit (if income more than basic limit) in those years.
Sec 44ADA - for Professional Income - Every person carrying on legal, medical, engineering, or architectural profession or the profession of accountancy or technical consultancy or interior decoration or any other profession as is notified by the Board in the Official Gazette are eligible for the presumptive scheme for professionals under section 44ADA. Declare minimum 50% of gross receipt as profit (or higher profit if the actual is more than 50%). Eligible professionals if Gross Receipt is less than 50 lakhs (75 lakhs in case cash receipt less than 5% of total receipt). He can opt 44ADA year wise i.e. No concept of 5 continuous AYs.