Payment deadline for undisclosed income requires notified payment, interest on late payment, and proof filing to validate declaration. The tax, surcharge and penalty in respect of undisclosed income must be paid on or before the date notified by the Central Government; the Government may notify classes of persons permitted to make delayed payment on or before a specified extended date subject to interest at the rate prescribed for delayed payment. The declarant must file proof of payment with the Principal Commissioner or Commissioner by the notified date, failing which the declaration is deemed never to have been made under the Scheme.