No interest can be levied u/s 234A if entire amount of tax has been paid on or before due date of filing return of income even if return is filed after due date:

If entire amount of tax on taxable income has been paid on or before due date of filing return of income, then even if return of income is filed after due date of filing return of income, no interest can be levied u/s 234A. If tax on total income has been paid in part on or before due date of filing return of income, then interest u/s 234A can be levied only on differential amount of tax (i.e. on total tax less tax already paid before on or before due date) and not on the entire amount of tax or else, it shall render the provisions of Section 234A penal in nature which the statute does not provide for.

[BHARATBHAI B. SHAH - SCA 9820 of 2002 - GHC]