Suppose I'm a professional like doctor, lawyer, consultant or architect and my income is 15lpa. I'm allowed to deduct business expenses like maybe uniforms, equipment, office rent, conveyance to arrive at taxable income.
I can deduct the whole 15lpa as expenses provided I have receipts of business expense and maintain books of accounts.
Section 44ADA of Income Tax Act allows me to deduct upto 50% if my income is below 50 lpa without providing receipts and maintaining books of accounts.
So from 15lpa, I deduct 50% and arrive at 7.5lpa as my taxable income. I further deduct 1.5lakhs as 80C (PPF, ELSS, NPA). Hence I'm supposed to pay tax on 6lakhs only.