Sub section 2 of section 44AD says that Any deduction allowable under the provisions of sections 30 to 38 shall, for the purposes of sub-section (1), be deemed to have been already given full effect to and no further deduction under those sections shall be allowed. which means that depreciation u/s 32 has already been allowed. You dont need to maintain books doesnt means that you dont have to calculate any figure every one who is doing a business should maintain a rough profit and loss account in which he calculate his profit and loss. Section 44AD says that if you file your return of income under 44AD you are free from maintaining proper books of accounts as mentioned in 44AA. You can easily find by every year making a balance sheet and writing wdv or balance of all your accounts, if you cant maintain bills for 10-12 years and in 10-12 years any asset value will be near to zero.
You must maintain basic profit and loss and balance sheet through which you can derive your profit.
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