Self Assessment Tax Must Be Paid Before Filing Return!
There is no provision that a person can pay less in a year and in succeeding year he/she pays more to adjust.In fact , if you pay less than what you should pay as per your computation of tax before filing Return , your return may be treated as defective return as per the Explanation to the Section 139(9).
Further the self assessment tax is responsibility of the person filing the return . The provision is contained in section 140A states as under:
However, what practically may happen is that the A.O may not invalidate your return and processes the return u/s 143(1), you will be charged with interest u/s 234B and 234C of the I T Act.that too till the date of processing of return.
He will send you an intimation which is a demand notice in itself. You may be charged with penalty u/s 220 if the new demand is not paid within 30 days of service of notice.
So what happens if return of next years filed with refund claim ?
If that happens ,You can write to the A.O to adjust the refund of next year to be adjusted with the demand raised for previous year. Anyway, A.O can not issue demand . This is as per the refund till he recover arrearsprovision in Section 245 of the I T Act which is given as under :
- 245. Where under any of the provisions of this Act, a refund is found..........of the refund, set off the amount to be refunded or any part of that amount, against the sum, if any, remaining payable under this Act by the person to whom the refund is due, after giving an intimation in writing to such person of the action proposed to be taken under this section."



