For taxpayers with a 31 March financial year-end , the Tax Administration Act 1994 requires that annual income tax returns be furnished no later than 7 July of the following income year . This is a statutory deadline that applies unless Inland Revenue (IRD) grants an extension. Tax agents may have until 31 March of the following year to file returns for their clients. Links Standard Practice Statement SPS 24/02 – Extension of Time Arrangements I RD Website – Extension of Time Arrangements for Intermediaries TAA 1994 Section 37 - Dates by which annual returns to be furnished TAA 1994 124C - Tax Agents