Filing deadline for VAT returns: Forms ST 11A and XIII must be filed by 31 January for the assessment year. Dealers registered under the Delhi Sales Tax Act, 1975 must file Form ST-11A, and dealers/works contractors under the Delhi Sales Tax on Works Contract Act, 1999 must file Form XIII, together with their returns; the last date for filing these statements for the relevant assessment year is fixed as 31/01/2006.