I get fd interest. how to calculate under 44ada?

Rajakumaaran (Dr) (30 Points)

28 November 2016  

Dear sir/madam
I am general medical practitioner (practicing for the past 29 years) usually not keeping any receipts. I get morethan 2.5 lakhs per year from Bank FD interest for which the banks deduct TDS @ 10%.
If my declared gross receipts are 7 lakhs /year at 50% my taxable professional income will be 3.5 lakhs. I do invest in PPF+ LIC premium put together 1,50,000/- 
How do I calculate my tax? 
Should I keep receipts hereafter if I opt for 44ADA?
Thanks in advance :)